A message board or web site set up with the intention of trolling unsuspecting registrants. The reverse of traditional trolling, where the message board is invaded by trolls looking to cause mischief. In the case of a Fly Trap, the targets come to it.
"Hey did you see that message board? What a bunch of idiots! How can people be that stupid? I argued with them for days, and got nowhere!"
"Dude, the place is a Fly Trap. You've been trolled."