One time in 4 years I left the windows down on my Audi A6. A cat snuck in and pissed on the carpet. I sold the car and got my Crossfire. I guess I should thank the cat, but it sure did **** me off. (no pun intended)

On a side note, I used to leave the top off of my Wrangler all summer long. The only issue I ever had was finding spiders all over the place.