1) Trusting a well known backstabber. Look at their past games. Look at their tributes. If it goes something like this:
12th - I backstabbed you.
11th - I backstabbed you.
10th - I backstabbed you.
(etc)
..then you MIGHT want to consider not trusting them. If you're getting mail from other players telling you they're a backstabber and they know this because they played with them before, and you still trust them, then you're a f***ing idiot.
2) Doing everything your alliance tells you to do when you are the 4th or 5th one to enter the chatzy. You're being used for votes. The first 3 most likely have a F3 deal and they don't give a living crap about you unless you somehow win veto in final 4 and they have to fight among themselves. If you don't secure your f3 deal with anyone else and continue to do whatever the first 3 people tell you to do, you're a f***ing idiot.
3) Backstabbing your alliance to help the enemy alliance.. then end up being evicted by the enemy alliance. lol *clap clap* You're a f***ing idiot.
Vixxen, you're golden.