Trolling a bar.
Searching a bar for somebody to hit on or buy a drink for.
Usually done by self-obsessed or desperate men preying upon younger women or other men, depending on sexual orientation.
Bar Troller: "Hey baby, -insert cheesy pick-up line
here-, let me buy you a drink."
Bar Troller 1: Hey dude, it's Saturday night. We need some play, let's go bar trolling.
Bar Troller 2: Sounds good to me, I could use some booty