Point to be noted

This is one neat trick. You need an accomplice for this.

The person you play this trick on has to be a friend of yours. He/She must be sitting some distance away, minding his/her own business. The victim should preferably not be acquainted with your accomplice.

Start acting as if you and your accomplice are talking about the victim. Occasionally, point at the victim. As soon as the victim notices, look away and continue discussing with great interest. Do this a few times, and eventually the victim will get bugged up enough to walk over to you, and ask you what's up. At that point, talk to him/her about some neutral thing, just so that he/she won't feel bad. (You're mission is already accomplished)

The fun in this trick is to irritate your friends to the extent that they come over asking what's up. If you don't consider that fun, you gotta try it out first!