I like to find ancient, arcane texts written in indecipherable language, and then recite the most disturbing-looking passages aloud. "Klaatu barada nicto." Hang on, someone's knocking on my door...
There've been so many stupid things I've done, but to this day, the stupidest was when I was coming back from a holiday one year, and somehow ended up with a whole lot of weed at the end of a pretty wild night. So I though it'd be a shame to waste it, besides, I was in my favourite city, so I thought what the heck, I can smoke this by the morning, it'll be fun. So while my companions slept, I sat on a balcony smoking and communing with my favourite place in the whole world. I literally spoke to the town, felt its heartbeat, felt hugged by it, was one of the most incredible experiences of that holiday. Come morning, everyone's up, getting ready for the flight home and I'm completely incapacitated. Still had to go through the airport security and a five hour flight, it was awful.