Don't know if this is really the same as testicle only but....
Was going at it with wife dog style and was at the point of going to cum when she reached up and punched me in the nuts as hard as she could. I had the most powerful orgazam in my life. Longer (more contractions) and intense. Timing is everything as she tried it again other times and I ended up on the floor holding my nuts..... Not the same as first time.