1. Complain too much. It's one thing to occasionally gripe about your workload . . . but the more you complain at work, the more likely you are to say something that could get you into trouble.
2. Volunteer all the time. Going above and beyond IS a good way to get on your manager's good side. But CONSTANTLY volunteering to take on more work or pick up other people's slack will put you at risk of spreading yourself too thin or having people take advantage of you.
3. Talk politics. It's a bad idea since things can get heated . . . especially these days.
4. Dress inappropriately. Even if the dress-code at your office is casual, you still need to exercise SOME judgment . . . particularly in the summer.
5. Come in contagious. If your company doesn't distinguish between vacation and sick days, it can be tempting to drag yourself into the office and save your time off for something fun. But you're putting your coworkers at risk, and you're more likely to make mistakes on your own work anyway. So just stay home.