I'm sure I've done a load of stupid things, I mean really stupid things, because I go round the park with the guy on these forums called airtimecadet, he's one of my schoolfriends. Anyway if I was some potasium he'd be the 5molar acid... or for those not familiar with chemistry, him + me = bad, bad idea.
However, the only thing I can think of at the moment is folding your arms behind your head and closing your eyes on stealth. I have become pretty good at it so it genuinely looks like I'm sleeping. You gotta tense your face ever so slightly to cope with the launch. On SRQ you get a guy screaming his head off next to you looking chilled as a cucumber.
Oh and stampeding onto rides once they have just been opened... shouting OMIGOSH this is soo high on Det when I'm 2 foot off the ground...
Oh there was once we went to legoland and we got so bored of the lack of big rides that on the wave surfer, where you press a button to release a spurt of water to soak riders, we teamed up and decided who to soak on each ride.
Usually it was some poor woman, and they laughed and it was all good because it was a hot day. But near the end of the day, we soaked this one young girl and her father, who was a beefy bloke, got mad at us and shouted at us, with a few of his beefy friends, which was slightly scary. Then we got stopped by a security guard because he'd complained to the ride op.
That's about the most daring thing I can think of, but I'm sure we've done a lot more dangerous stuff in our time.
PS in case you're wondering, if we ever go back to legoland, we will do that again, just not pick on young kids. We've learnt that it's harsh and we won't do it again... much.