Trunk Monkey is a term used when talking about a women's urge to have hevy sex. The term is used usually when talking about the ting-a-ling feeling in a girls vigina, right before she has sex with someone.
guy 1-"that party was crazy"!
guy 2-"that girl was hitting on you so much"!
guy 1-"why was she all over me tonight"?
guy 2-"cause her trunk monkey wanted out"