(CNN)First there's the valet.
Awaiting your arrival with a welcoming smile, a claim ticket and a tacit understanding that you'll know how to properly reciprocate ($5) when it's time to retrieve your car.
Followed by the bellman ($2 first bag, $1 each additional).
And the concierge ($5 to $20, depending on the task), who can recommend several good bistros in the area and help with hard-won reservations.
Later, the taxi driver whisks you to your restaurant (10-20%) where the maitre d' has gone the extra distance ($10 plus, quietly) to secure the perfect window-side table with the sort of grace and palm-nourished professionalism rivaled only by your sommelier (discretionary), waiter (15-20%) and restroom attendant (a buck if you take the towel and mint; more for emergency supplies and quick marital advice).
Back at the hotel, your suite has been carefully prepared by an invisible but very much existent and equally deserving housekeeper ($2 to $5 per day).
And on it goes.
Spa therapists and hairdressers (15-20%).
Skycaps ($1 per bag, $2 for heavy ones) and tour guides (15%-ish is most appreciated).
And now, all of a sudden, let's not forget the dude manning the register at the indie pizza joint, gastro-pub or premium ice cream parlor who swipes your card and then swivels the screen around to let you discreetly e-tip a suggested default amount -- 10% ...15% ... 18% ... 25% ... and here it comes 30% (for over-the-counter grub) -- while he politely looks away.
Yes, there's also a "No Gratuity" option at the bottom of the screen if you're that person.
And not to worry.
No one's judging you to your face.
Whatever you feel is right, pal.
Is there anyone you needn't tip on your next trip to the States aside from the guy at customs (not recommended)?
"Servers work in the U.S. with the expectation to be tipped -- it's a social contract," says Cornell professor Michael Lynn, a specialist in consumer psychology and the socioeconomic impacts of tipping.
"To come here and accept the service of these people, visitors are implicitly accepting those terms. To tip in a manner consistent with our norms."
Not that they always do.
Or are legally required to.
No one is.
Americans don't need laws to dutifully dole out more than $40 billion annually in restaurant tips alone according to economist Ofer Azar.
Or to espouse a once-reviled, centuries-old institution imported (and more or less deported) from Europe where service charges and loose change have largely taken over.
Tipping was once so hated in America that six U.S. states officially outlawed it in the early 20th century.
The practice once spawned an Anti-Tipping Society of America (lobbied by traveling salesman) and has been branded "un-American" in at least one Humphrey Bogart movie.
And, yet, tipping in America has survived all that. And thrived in spite of it.
Today, Americans love tipping more than ever.
At least that's what mystified visitors to the U.S. might surmise -- not entirely correctly.
A recent Cornell study shows that 44% of Americans would prefer restaurant waitstaff be paid higher wages instead of relying almost entirely on tips for income.
Most states allow employers to claim a "tip credit" which can effectively reduce their minimum hourly wage obligation for tipped employees to as low as $2.13.
Ubiquitous tip jars
On the other hand, 95% of Americans still prefer tipping over an automatic Euro-style service charge added to the bill -- an increasingly popular move in domestic tourism industries like cruise lines (and hub cities like Miami) that attract foreign clientele who either don't comply with U.S. tipping norms or begrudgingly do but wish they didn't have to.
"Oh, how I hate the American tipping custom," laments a New Zealand businessman on traveller.com. "I just hope Americans can be understanding of foreigners who either don't know or understand the system, or simply don't have small denomination cash on them."
"I think it's awful that these people have to rely on tipping to make a decent wage," posts a VirtualTourist international traveler in New York City. "We will tip the expected amount, of course, but I just feel it's a lot to add onto our bills."
All grumbling aside, what is the expected amount to tip in the U.S.?
And why is 25% suddenly the new 18%?
And should those ubiquitous tip jars at every cash register be weighing on one's conscience too?
Is there a failsafe U.S. tipping guide that can neatly answer all those questions?
"There is no definitive guide to tipping," says Lynn. "There have been a number of studies done on tipping guidelines and it's actually kind of complicated—not at all straight forward."
Lynn's studies have, however, found a lot of consistency between the general figures listed in guidebooks or online with what real people actually tip according to smaller-scale academic studies.
Americans, he also notes, aren't just tipping for the classic reason (to reward good service) but for several others -- including social approval, guilt reduction and an overall sense of basic duty and moral obligation.
The good news, if you're just visiting, is you can set all those reasons aside.
But you should still tip, within reason.
Not 30% for an already pricey waffle cone.
But not a measly 10% for a meal unless you're truly unhappy with the service or pretending it's still 1958 (in Ohio, not Copenhagen).
"Research shows that people tend to take their tipping habits with them," says Lynn. "The bigger disparity between what they're used to and the culture they're traveling to, the more perplexed they'll be."
But that's not you.
Here are some helpful tipping points to store with all those small bills.
Food and drink
Tipping 15-20% of the bill before tax ("some would say 15-30% now," says Lynn) is the average range for waitstaff, skewing higher for great service. Leaving 10% reflects substandard service, zero abominable.
The old "two pennies on the table" statement just fans flames. (It's a not-so-sly insult that let's the server know you didn't merely forget to leave a tip.) If need be, speak to a manager instead.
Bartender: $1 to $2 per drink or the same percentage on your tab as you'd tip a waiter.
You don't normally hand over a tip directly to a waiter or bartender.
Although the practice astonishes some international visitors (who perhaps assume lawlessness lurks around many a corner in the United States) it's standard practice, once your bill is settled, to simply leave the tip on the table or bar top and leave. No one will steal it.
No obligation for takeout, but 10% for special service like curb delivery or larger orders is good form, says emilypost.com.
Delivery people who come to your door -- pizza and Chinese restaurants are typical -- expect 10-20%.
No need to pay for smiles, doors opened or highlighting a city map. Or to tip each individual member of the bellman tag-team between curb, lobby and guest room.
"Give one handout ($1 to $2 per bag) when you've reached your room," says budgettravel.com.
Tipping the hotel maid daily ($2 to $5) -- directly, under the pillow or with a little note marked "housekeeping" -- ensures the right person receives it and that your room looks the part during your stay.
Room service: tip at least $5 unless gratuity is included in the check, says businessinsider.com.
Valet: $2 to $5, generally when the car is returned to you.
Courtesy shuttle: $1 to $2 per bag if your driver helps you with them.
Taxis, limos, vans and paid shuttles: 15% of the total fare and up to 20% for above-and-beyond service, advises tipguide.org.
Head to heel
Hair: 15% will suffice but the "cardinal rule" for salons is 20%, says stylelist.com.
Same range is customary for your massage therapist at the spa.
Shoe shine: 10% = Unhappy. 20% = "We're good." 30% = "Wow." 40% = "You've just made my day, I want to make yours," translates a seasoned New York shoe shine person to esquire.com.
Last few tips
Before tipping, check that a service charge hasn't already been added.
Tip discreetly, respectfully and from the full amount if you use a coupon or gift certificate to offset the bill.
When in doubt, you're allowed to ask (preferably the receptionist or concierge, and not the person you'd actually be tipping) if tipping is customary and generally how much is appropriate.