this is usually said by a cheating partner as an inside joke to the person he or she is cheating with. it is meant as a joke about popping up and saying boo to the cheating partner's significant other, which obviously can't be done.
"tell your man i said boo. when are you going to leave his broke ass for good so we don't have to sneak around anymore?"
by justin8239 February 16, 2009