When a female finds something either sexually arousing or expresses much interest in something (usually food) that a male would typically agree with.
Example 1
Boy: Katie was sooo hot when she kissed Mandy
Girl: omg that just gave me a theoretical boner!
Example 2
Boy: Did you hear they have deep-fried twinky's at the fair this year?
Girl: Wow the thought of a twinky deep-fried gave me a major theoretical boner!