When you go on twitter and look at people's followers, clicking on one of them, and then again on one of their followers, and so on, ad infinitum. For men this primarily takes the form of clicking on what looks like the hottest girl in the tiny little pictures of twitter followers.
Cf. also twitter creep, twitter creeper, and related usages.
"Look at this unbelievable babe."
"Dude, you're twitter creeping again!"