(1)When you are/are not in a relationship. and have a person you fuck on the side. Side duffs manly are just people who you don't really care about, but just only to fuck.

(2) Someone who likes/loves you a lot and buys you stuff and is always promised sex, but never get any in return.
(1) monica was Bill Clinton's Side Duff
by Pititfulfilth March 16, 2011
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