Ways not to lock your bike

Current suggestion is to buy a replacement lock, cut this one off, lock up the other bike with the new lock and take the key leaving a note to not lock other people's bikes up.

And smear a bit of poo on the handlebars, obviously?

Bit late I know but if that happened to me I would just cut the lock and if I was feeling generous (unlikely given what has happened) I would try to arrange the cut lock so that it looked like the bike was still locked. If I was in a really shitty mood (much more likely) I would leave the bike blatantly unlocked with a note on it that said "for free".