Here's a couple cell phone games to try, which can be amusing if you're with another person or two; but be warned that also makes it hard not to laugh while you're doing it. This is something you'd expect to see on the TV show "Jackass".
1) If you're in a public place, and some idiot is loudly blabbing on thier cell phone -bluetooth or not - stand near them and quickly grab your phone, hold it up to your ear, and start answering or replying to whatever that person is saying, just as loud as they are. Pretend you're talking to them. The person you're mocking will NEVER catch on - and you'll be entertaining the people you're with.
2) This one is a little more brazen and bold - but if pulled off right in the right setting, it can be extremely entertaining if you're with other people:
Say you're on a plane - just blocked in at the gate, everyone's standing up, waiting for the aisle to clear. Grab your phone, pretend you dialed your spouse.... say "Hi honey, my plane just just landed. Did the Lab call about my TB test results?" Or, "You won't beleive this - the clinic said I AM contageous and I should get home to bed".
Or, in various settings, here's some other good ones....
"Guess what? My rash is getting worse - the left one is all red and itchy"
(Pretend you're calling a pharmacy) "Hi, what do you recommend for Hemmorhoids?"
"I've made up my mind; I can't live like this - I'm turning myself in - I'm going to the police right now."
"No, no, no there's no need for that. I'll pay you 20 thousand in cash today and 80 grand by Friday"
"Well it IS a problem now - because my wife found out about it"
"Everyting's taken care of exactly like we talked about. I assure you they will not find his body"