My favorite thing that a girl has done during sex?
I don't know whether other men experience this (and I'll be interested in any comments), but when I'm about to cum, I reach a moment when I have to thrust firmly all the way into the woman's vagina, and then hold there while I let my seminal vesicles, prostate, and their associated muscles take over and start pushing my semen out.
One ex-GF learned to use my stopping stroking as a signal to her to start milking my penis from its base to the head. She would do this with strong, smooth ripples of her vaginal muscles, which were naturally tight (thanks to her regular Kegel exercises), and the milking enhanced her natural tightness in an extraordinarily exciting way.
Her special talent never failed to bring me to a lovely orgasm.