Restaurants do not include a service charge in the bill, so you should tip the waiter 15% of the total bill. If service was slow or particularly bad, some Americans will tip only 10%. Likewise, if service was particularly good, it is appropriate to tip 20%. If service was so bad that you would never eat in the restaurant again, leave two cents. This is a deliberate insult, because it tells the waiter that you didn't forget to leave a tip. Tipping is only appropriate in restaurants which offer table service. You do not tip the cashier in a fast food restaurant.

The words "tip" and "gratuity" are used interchangeably, with "gratuity" having a slightly more formal connotation.

Taxi drivers expect to get a tip equal to 15% of the total fare. If the driver was especially helpful or got you to your destination more quickly than you expected, give a 20% tip.

Hotel bellhops expect a $1 tip for helping you with your bags. If you order room service, the gratuity is included in the bill. Coat checkroom attendants expect $1 per coat. Hairdressers and barbers expect a tip of 15% of the bill. Valet parking attendants expect a $1 tip.

Federal regulations prohibit letter carriers from accepting cash gifts in any amount, or gifts worth $20 or more from customers.

If you are in doubt, ask whether it is appropriate to tip or whether a gratuity is included in the bill.

Bribery is not considered appropriate and often illegal. Attempting to bribe a policeman will certainly get you arrested.