A wide range of things...anything from underage drinking (very common) to physical contact (I know people who got termed for shoving roomates etc) to getting 4 warnings.
yea, underage drinking is the most common....one guy from the Italian pavilion got terminated because pee around the commons! and last week 10 french guys got terminated because they got into a fight right in front of the security!
Some people I worked with almost got termed for peeing in bushes outside HoB. So... erm... control yourselves folks (They didn't, but apparently they came very close) Stealing (absolutely TONNES of people got termed from the treehouses over summer for this), underage drinking (although they can be more reasonable about being caught for doing this than you might think... again not that I'd encourage it. Ahem), warnings/points (mostly gained from too many call ins or clocking in/out late) and other things that it should basically be common sense NOT to do...