1. Eating smelly food at your desk. Some of the worst offenders are hard-boiled eggs, broccoli, tuna, and seafood in general.
2. Asking too many questions. Asking questions is fine. Just try not to ask too many work-related questions, or you'll look like you can't figure stuff out on your own. And asking a lot of PERSONAL questions is risky for other reasons.
3. Being a slob. A messy desk is one thing. People might judge you, but probably won't hate you for it. Just don't be a slob in common areas, like the kitchen. It makes you seem irresponsible, arrogant, and immature.
4. Interrupting people all the time. You can definitely interject. But in general, make sure you just respect people enough to let them finish a thought. Otherwise, it looks like you don't have good judgement, or you're impatient.
5. Talking to people in the bathroom while they're in one of the stalls. At the sink is fine. And the urinal, still fine. But if they're in a stall, leave them alone. It just feels awkward and intrusive.