Haha. I usually hit the guy with the RPG right before he hits me. If it's from a distance I usually take a few shots and if I didn't get him, back up and wait for the RPG to come in, move forward and take a few more shots. Repeat until I die or he dies.
Recently, on the 24/7 dust2 server, I've noticed an increase in boosting onto the roof and boosting into the Marine spawn. I believe you can be kicked or banned for doing this.