Tipping is such a weird thing. Now that we've admitted that, we can acknowledge that it's this very weirdness that makes the need for rules and manners in society — they help us deal with the things we don't know how to deal with. 

When it comes to tipping, though, it can be hard to know what to do. MNN blogger Robin Shreeves admits that she "guilt tips" regularly, and I always err on the side of overtipping — except if service is poor, and then because I used to be a server, I'm pretty harsh. On the other hand, I would be in favor of eliminating tips for waitstaff (and paying them a competitive wage instead), because overall, I think most servers do a great job and shouldn't lose income because some people are cheap jerks. 

Then there's the gender aspect to tipping, which Maria Shriver got into recently, helping Marriott institute what I'll call a tip-encouragement program: The hotel chain will now be gently pushing people who stay in their rooms to tip their housekeeper in the The Envelope Please initiative.

"I was talking to room attendants, who were overwhelmingly women, and they would tell me that people were pretty sophisticated about tipping the bellman or concierge, but they hadn’t been educated that they could leave a tip for a room attendant," Shriver said in an interview with The Boston Globe.

So, who should you tip? And how much? I've combed the Internet advice columns, and checked out the individual proffessional's notes on tipping too—and added a hearty dose of my own tipping proclivities as a world-traveller and homeowner—to come up with this list. I hope it helps you next time you're feeling nervous about how many dollar bills to pull out! (Note that these are minimums, and you should feel free to tip more for great service from anyone.)

Bars/restaurants/coffee shops

  • Barista: $1 per handmade coffee (espresso, cappuccino, latte, etc.) as this requires skill and training; 50 cents for pre-made drip coffee or tea
  • Takeout : No tip (unless they do something special)
  • Waiter: 15% is standard, 20% for good service, more for great. 10% or less if service is poor (and you know it's the waiter's—and not the kitchen's— fault)
  • Food delivery person: 10% or at least $3 (more if it's raining, snowing or otherwise inclement weather)
  • Bartender: 15% is standard, but 20% is more appropriate if you are ordering complicated mixed drinks
  • Sommelier: They get a portion of the tip for the whole bill in most restaurants
Hotels
  • Porter: $1 per bag, $2 minimum
  • Concierge: Depends on service. For the basics (directions, maps), nothing is fine. For more (reservations, wrangling tickets to a show, etc.), $5 for something easy, $20 for something challenging
  • Housekeeper: $2-$3 per night, and it's ideal to leave the tip in cash each day, since housekeeping staff can rotate day-to-day. However, leaving a lump-sum tip at the desk upon checkout is better than nothing at all. 
  • Valet: $2-$5 when your car is retrieved (pre-tip if you hope for faster service upon leaving)
  • Room service: 20 percent of the bill, but be sure to check to see if they have already charged a gratuity for this service; many hotels do. 
Transportation
  • Bus driver: $1-$2 per bag handled. (If it's a tour of some kind where the driver is also the guide, see below.)
  • Guide: $10-$20 for a several-hour to all-day tour, $20 a day for multi-day tours
  • Cab driver: 15 percent for good service
  • Other driver (limo, car service, rickshaw): 15-20 percent(higher for more personalized service, local info, etc.) 
  • Train attendant: $5 if they help with bags or otherwise assist you
  • Porter in a train or bus station or airport: $2 a bag
Hair/nails/massage services
  • Hairstylist: At least 10 percent, but 20 percent is probably more appropriate if the person does good work, takes their time with you, and you see them regularly
  • Shampooer: $5 minimum (unless it's an inexpensive haircut, in the $20 range, in which case $2-$3 is OK); $10 is appropriate for any haircut over $40
  • Manicurist/pedicurist: 15-20 percent (higher if there is nail painting or very funky feet involved) 
  • Facial, body wrap, massage therapist: 15-20 percent
Random other people to tip
  • Coat checker: $1-$2 per coat
  • Large-item delivery: $10 for a regular delivery, $15-$20 if they have to maneuver up or down narrow stairways, etc.
  • Mover: $20-$40 depending on the size of the move and the number of hours worked
Yearly tipping

Some of the people who provide regular services to you only get tipped once a year, usually around the holidays. (I tip at New Year's since I'm not religious and call it "Thanks for work done in the prior year" which means I won't make an error about someone's religious beliefs.)

  • Mail carrier: Don't tip in cash, it's illegal. A $20 gift card is appropriate unless he or she went above and beyond, and then something more would be nice. If you know your mail carrier (and you should!) you can also just get them a gift you know they'll like. I give mine yoga gear. 
  • Garbage collector, parking attendant: $20
  • Housekeeper, gardener, nanny, personal trainer (aren't you lucky!): one week's pay as a year-end bonus
  • Your kid's teacher: Gift card in whatever amount you can afford
And don't forget: If you use a coupon, gift-card, gift certificate or take advantage of a Groupon-like offer, your tip should be based on what the bill would have been before you used the discount.

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Starre Vartan ( @ecochickie ) covers conscious consumption, health and science as she travels the world exploring new cultures and ideas.