My girlfriend and my best childhood, and only remaining real friend these days, cannot get along. All they do is fucking fight , its always something trivial like him rolling his eyes at something she has to say. And her getting upset about it and him denying it or whatever. I like to go to the weekly lan party with them both but its getting real difficult and I don't know what to do anymore. I have told them both several times to grow the fuck up about it. Now I'm just at a loss.

hmm.... try and talk to her about it.. and talk to him about it, and tell them both, that their fighting is effecting you..

or just hangout with them at different times... or kill them both, its your choice

kill them both came to my mind. But really I want to hang out with them both at the same time. Because they're both my friends you know?

You just have to talk more.
"Grow the fuck up" tends to immediately start some sort of defense in whoever you're talking to, even if it's only to not take what you're saying seriously.
Really talk to them both. Talk to the girl and let her know that this guy, (who can probably be a dick sometimes like most people), is your friend, your only real friend left from childhood, and you'd like to keep it that way if at all possible.

Make sure the friend understands the same, the girl can overreact to his words/actions and get bitchy about it, which you then have to deal with. The guy's actions either stem from him not giving a shit about what the girl says or just disregarding it... at worst... to just being a friendly jokester kind of guy with the kind of humor your ladyfriend just doesn't understand.

Just seriously talk to them and they'll probably agree to put some effort into... growing the fuck up.

If he were really your friend then he'd make a superhuman effort to get along with your GF for your sake.

Or if that really wasn't possible he'd voluntarily not be around when she's there.

Real friends put their friends happyness above their own. Ergo he isn't your friend so ditch him.

Tell them there are some basic rules when you're all hanging out. No bitching, no being a sarcy bastard, no pathetic squabbling. Or else you're going to go find yourself some new friends.
People arguing is inevitable, but it's fucking wrong for them to do it when everyone else is trying to have a good time, because they ruin that.

My brother's woman hates me...I make him do terrible things like go out, have a drink and laugh. She's a stupid bitch...She texts himand threatens suicide unless he comes home.

But anyhoo...

I would be "the friend" in this situation...I stay away...If I don't see her, I can't piss my brother off.

Keep the petrol away from the fire and nothing bad happens mate.