My learned friends at the Gay Academic Union in NYC called it irrumation.

What the heck is that? Well, it's like that other thing, fellatio, except that the "top" does not lie back and passively accept sexual pleasure, but agrees with his partner on an active role. Other people call it mouth-f*cking.

Is there a better word? The main reason I ask is that so many "straight" Thai boys enjoy doing this -- and enjoy it enormously. I remember clearly the day when I suggested this to S., some 15 years ago. He blinked his eyes, as if to say "really?" and went right at it with a viggah which I enjoyed very much.