Obvious, my dear Watson

This irritant is simple but may not always irritate the victim.

When you meet your friend somewhere, ask him/her some obvious question.

For example,...
"You have class today, do you?" (Why else has he/she come to college today?)
"Drawing class?" (Why else is he/she carrying the drawing equipment?)
"Had lunch?" (Why else is he/she walking out of the restaurant at 2 in the afternoon?)
"Playing tennis?" (Why else is he/she carrying the tennis racket?)

Unfortunately, most of these questions are considered good conversation starters! So, it'll work only on those you don't need conversation starters to speak to. In other words, your close friends! You're likely to get a lot of creative answers, too!

"You have class today, do you?"
<> "No, I came here to eat canteen food."
"Drawing class?"
<> "No, I'm showing off this equipment."
"Had lunch?"
<> "No, I don't eat."
"Playing tennis?"
<> "No, I gotta kill cockroaches."