No, there's a method to their madness. They use it to build a bankroll from something smaller than might be smart to buy-in with.

Watch how they play when they're at your table.

Ace-paint (any Blackjack) hand plus any pair AA-TT is raised pre-flop to $1 (4xBB). If they only have $5 in front of them, now you don't have the odds to call them with your lower PP hoping to bust them when you get trips, let alone calling them with SC or Ax suited. If you call, they win, according to the Fundamental Theorem of Poker.

OK, so say you call. Unless the flop completely misses them and is coordinated, they push in. At this point, that's probably a pot-sized bet or bigger. Since most drawing hands don't hit a flop well enough to call getting 2:1, and there are absolutely no implied odds from this point forward, it's almost always incorrect for you to call. Again, they win according to the Fundamental Theorem of Poker.

The only way to combat this is to actually have a hand preflop or fold.

Watch what they do when they get up around $15. They leave the table. Why? Take their profit out and move to a different table for the minimum buy-in again.

I haven't actually tried this, so I don't know if it works. It seems like it would show a profit over the long run as long as someone calls most of their preflop bets.

I have busted plenty of them. If I have any sort of a hand (anything comparable to what they'd raise with preflop), I'm putting them in pre-flop. Bust 'em once and they tend to leave the table. If they happen to get lucky once and have AA when I put 'em in with my KK or QQ,well, they only get $5.

phish is right. Some of them are big winners because people keeps calling them because it s only 5 or 10. Most of them are winners but you can kill them if you play exactly like phish said. I let them take my blinds for a while and then I push with AA-QQ-AK. Sometimes I even pushed with 99-88 if they are very aggressive preflop. Most of the time you have them beat with 99. it s for sure a coinflip but it s worth it to take them out and have a real stack at the table