Collect five bar straws. It is important that you have five for this trick, as it will make the trick. Having too few will ruin the gag and too many will be confusing. Keep these five straws with you and wait until the right moment to use them.
Look for a person or group of people who look like they will appreciate some crude barroom humor. This is a good way to get to know a bartender but is also an excellent introduction to another person sitting at the bar. Use your judgment, and don't choose people who look like they want to be left alone.
Go up to this person and say, "Can I ask you a question?" Wait for the person's response. If they are in a group of people, pick the most boisterous and outgoing of the bunch to ask. Ideally, they will say "OK." Then you ask them, "I bet I can make something round out of these five straws, can you?" If you want to spice it up, bet them a drink or a dollar.
Let them try to make something round. Tell them that they cannot bend the straws, and they must use all five. They will try all manners of designs, but none will be round.
Show them the solution. Arrange the straws so they spell the word, "Tit."