Although meetings can be informal, showing up to one looking like you just rolled out of bed is not appealing. In fact, showing up to work looking sloppy every day is not appealing, period.
6. Playing hooky
We all take a day or two off work when we need it--whether it be for emotional, illness, or personal reasons. Doing this often--and on days when you know there will be meetings at which you should be present--reflects poorly on you.
7. Playing with your phone or laptop
You should not text, play games, browse social media, or check sports scores while in a meeting. It shows an utter lack of respect for the time of everyone around you trying to make things run efficiently.
8. Interrupting
Waiting your turn to speak up is necessary to show that you are both paying attention and respectful of the opinions of others. Don't downplay the fact that you are able to do both.
9. Swearing
No matter how casual your workplace can be, it's important not to bring that culture to a space where people are working to be as professional as possible. Save the curse words for after you clock out for the day.

Thank you to Peter Economy for writing this article.