HO = Head On PASS...emphasis on the PASS part. Do
not remove the P.

Thats my new AH2 interpretation (now I just need to convince about 8000 other guys hehe)
However, if it's just a random encounter and there's a pass, there will be rounds fired at your windshield and engine. I don't care who you are, because if you don't challenge me to a duel and you do a head-on pass, you're getting exactly what you deserve.
This is just silly.....its MY FAULT? You pull the trigger and its MY FAULT? Keep yer grubby little fingers off the trigger for one pass and have a little fun will ya? Are ya skeered you might enjoy yourself?

in a one on one its just a cheap shot.
I dont think so, not after the initial pass. Not in a furball or outnumbered. Its not really a cheap shot at all, my problem with it is that it will probably end the fight immediately for one or both participants. Thats not fun. There may be times that it is deemed necessary, but I'd never say its fun. I do it once in a while too, but cant really say I enjoy it.
Good points made by others above about deflection shots and quarting merges.
My first day in the game I upped a 190A8 and did nothing but HO's. Know what? No one ridiculed me for it, mostly they avoided and then shot me down. They also helped me with lots of advice. None ever said "Stop HOing". This was in 2001 and these were experienced and respected players (Shane was one, another was a 38 driver of some reputation at that time. Cant be sure who it was though.) Point is I was a clueless noob, even more clueless than most, doing what most folks seem to hate the most about noobs and wasn't treated like a noob.