1. Showing up late a lot. Your boss isn't the only one who notices. Pretty much everyone does after a while. And people WILL gossip about it.
2. Complaining about every little thing. Whether it's work-related or personal stuff.
3. Asking too many questions. You just look incompetent, like you're the weakest link. And people get sick of having to help you do your job.
4. Being messy. Which might mean a messy desk, or leaving old food in the fridge.
5. Being arrogant. Especially if you start acting like the boss and telling people how to do their job.
6. Bragging. You can do it in your annual review. But you shouldn't do it in front of your co-workers all the time.
7. Not dressing up for work. A lot of jobs don't require a suit and tie anymore, but you still shouldn't show up looking like a slob.
8. Getting too personal. It's easy if you think of your co-workers as friends. But things like family problems and your sex life should be off limits. At least during office hours.
9. Being loud while people around you are working. Especially if they're on the phone.
10. Swearing all the time. Even if your company is pretty laid back about it.