[monk]

True plus a small key is likely to get caught by the wind.... stick it in a sock or attach a keyring to it.

If you want a forced into it type of dare:-

Put a 'spare' door key under a plant pot or something outside. Then a little later strip down to your underwear / nude / cross-dress or just a towel (what ever you want really,) now walk outdoor and close it behind you.

If you've put the key out of site or put it out the night before etc.... then you'll have the fun/excitement/dread of not knowing if the key is still there!!!

Plus once the door is closed you'll have little choice but to go get it, if anyone spots you just say the door closed behind you.