Is it possible for any guys to piss while you are really really hard?
It is not impossible but it is also not a good thing given that your dick is pointing up at a 45 degree or so angle. Makes for a rather odd fountain.
I have managed it in an emergency by sitting at a very weird angle on the toilet but this is not recommended procedure.
The couple guys I've tried to aim while really hard, couldn't get a flow unless they let it soften some. Didn't know if this was the way every guy was plumbed or not.
Only if you piss in the bathtub or outside.
Yes, but a little more concentration required.
Can be good for "clearing the pipes" after sex.