The above pyro suggestion isn't a ping thing. It's an issue with how airblast targetting works.
Right now, when you airblast, say, a rocket, it finds whatever your crosshair is pointed at (potentially the inside of a teammate's model if you're inside one another) and aims the rocket at that point in space. Thus, if you are inside a dispenser or a teammate or something, you can redirect a rocket to yourself. This is also why you can airblast a RJ-ing soldier and he'll get hit no matter which direction he fires.
It should just note where in the airblast it was hit, and then travel from that point in the same direction you're looking.
Given that the client sends that exact information to the server with every packet, this should not be difficult to implement.