Coworker flipped me off. What should I do?

Just ignore him. Be nice to him. Kindness always comes back in ways you won't expect. Just don't be rude back. And most importantly, forget about it...

In my personal response I wouldnt do anything. Just because you were flipped off doesnt mean that you have to retaliate. Sometimes no response is the best response. It shows that youre more mature than that and can handle situations well. Im not saying to allow youre coworker to walk all over you. But in this case noone was hurt & its best to leave things as they are. You clearly see how that person feels about so youll have to stay out of each oters way. If it comes to a point where the coworker is constantly bothering begin to collect evidence and report to the boss or deal woth the matter in a different way. :)

Let's look at a few options, and see which makes most sense. 1. You could attack the co-worker, physically or verbally. People of course do that as a matter of course, and sometimes find themselves in legal trouble, or fired. Probably not the best choice. 2. You could flip them off the same way they did to you. Unlikely to get you into legal or job security trouble, but likely to build extra animosity. When someone attacks you, they made themselves an enemy. When you return the attack, you have made yourself an enemy. 3. Another option might be to just avoid the coworker. If you aren't in danger, this is usually the safest option. Unless you think it may happen again (in which case you might speak to a supervisor or HR for help) the easiest way to deal with these things is usually to let it go. That doesn't mean you must "forgive and forget". That's your call. Best of luck to you!