Literally this expression refers to the adhesion of one's penis to one's thigh in an attempt to tame an insurmountable erection. The expression is used figuratively to inform another individual that he or she is exhibiting behavior demonstrative of elevated levels of arousal, excitement, or enthusiasm. The variant "tape it to my leg" is useful when preceded by the phrase "you got me all boned up and now I gotta...", as a way of expressing resentment for an individual who has unduly excited one and left one unsatisfied. Also popularly used in a wilderness setting, or in the absence of tape, "strap it to your leg".
Whoa, easy there bronco chief, tape it to your leg!, Damn, girl, you got me all boned up and now I gotta tape it to my leg.