honestly, you need to do something about it instead of b!tching about it at this point if it's bothering you. It's different when you have no control over the situation; but you can take action in this matter.
You felt like he was *********ing, then posted and let him finish. If you go up now and say, 'yo man, were to *********ing?'
you look like a little b!tch. If he says 'you knew? and you didn't stop me? wtf is wrong with you man?'
Damn man.... i think you should just chill and act like you didnt know he was doing it. Like you said the man was blowing off steam...... fapping is actually thereputic helped me cope with being neg repped....