Heads and shoulders

A blonde and a brunette are catching up after having not seen each other for a long while, when the brunette says to the blonde, “Did you know that I’m married to Billy now?”The blonde replies, “Really? No, I did’nt know that, but I used to date him. Isn’t he the one who had the really bad dandruff?”“Yeah,” answered the brunette, “but I fixed that, I gave him some head and shoulders.”The blonde looks really confused and after a few moments asks, “How do you give Shoulders?”