This seems disturbing because it was very visible and blatant (although probably harmless college guys who were laughing it up). I actually think there is significant risk playing off the beaten track from the regulars. When you have a finite number of players, it is fairly easy to prey on the newcomer regardless of their skill. Having said that, teams are everywhere, for sure in Vegas. I've witnessed a couple of troubling events while at the Bellagio on two different occasions. In big rooms like that where it is extremely busy, policing this type of activity can be difficult. The raise/re-raise to get player A out of the pot then checking down is one easy tell. Another more blatant (similar to what you said) was a maniac next to a guy, maniac lady three-bets folks out of a pot then says, "let's chop the pot." The blatant one's jump out at you, it's the invisible one's you have to be alert for...