During intercourse a man will lather his dick (aka shaft) and balls in peanut butter and jelly. Once the man has successfully coated his dick and balls in the famous pair he will then put the whole package between two nice fluffy pieces of white bread and let the girl eat it all off. Voila, you have a PB and Shaft.
Dude I was having sex with my girlfriend last night and we decided to get a little bit frisky, so she let me try out the old PB and Shaft trick. I've never seen here eat so vigorously.