I have no problem as long as it doesn't interfere with him paying attention to me later
Sometimes you just gotta have it, and the other person's not around, or sleeping soundly and you don't want to wake them up. Heh.
I've never understood the taboo about masturbation, and I don't understand why some people have a problem with their partner masturbating, as long as it isn't otherwise interfering with their sex life.