Top definition
A slight fluttering sensation felt in the flaccid penis as it starts becoming erect during normal everyday activity or while seated, usually as a reaction to some kind of unanticipated sexual stimulus. The trouser butterfly is also associated with a very slight movement of the penis as the erection progresses, making a noticeable movement through the trousers / pants.
Did you see that gorgeous new receptionist? She was so hot it gave me a trouser butterfly.

I got a trouser butterfly on the bus this morning because the seat was vibrating so much, and I'm sure the woman sitting opposite noticed.

Sandra asked me out for a drink at lunchtime - it gave me a trouser butterfly just thinking about it!

by Killdozer May 01, 2007
Mug icon

The Urban Dictionary Mug

One side has the word, one side has the definition. Microwave and dishwasher safe. Lotsa space for your liquids.

Buy the mug