This isn't a contest though. People need not be pressured to draw well to be able to participate. One could probably come up with a comic featuring stick figures but as long as it is funny, it wouldn't matter.
As for a theme, this is simply a suggestion, but how about a 4-panel strip of a humorous event/conversation that you've experienced in real life? Kind of like greentext stories on 4chan, only in comic form. I'm not really too keen on making and setting up my own joke for a comic, since I'm just not a very funny person to begin with, so it would be easier that way to derive the comic idea from a real life exchange.
I kind of do like the idea of something CL-related as well though.