Problem with an ex friend...?

So, there's this person i used to be friends with. He shared details of his life with me. We were friends for about 2 years. The thing is that he was spoilt and said bad things about everyone around him. So one day i got tired and told him i didn't want to be friends with him no more. So he went to facebook and called me names. Just like he does with people who say things he doesn't want to hear.

Thing is, we have a common friend, and i'm afraid that i see this person when i go out with her. Chances are it'll be really awkward and the guy's kinda crazy so yeah. So what should i do? Think bout this? Not think bout this? Please gimme some advice.