Those dancing flowerpots (or Coke cans) that have a motion and/or sound sensor. I like to play doctor first though and make sure that the on/off switch is permanently set to 'on'. I gave one to my brother many years ago, and despite his reverse operation to make sure he could turn it off again, his wife loves to turn on the motion sensor so that when he gets up to go the bathroom at 3:00am, he nearly makes his deposit before leaving the bedroom. She won't let him throw it away.
For Kids: Remote controlled toys. Specifically there is this really cool robot that makes about a hundred different noises; all of which will send a shiver down your backbone. I gave this to one of my best friends kids many years ago and I made sure that I included at least a years worth of batteries. The kid was also old enough to know that there were spare batteries, so the usual parenting excuse that there were no batteries simply didn't fly.
More for Kids: Fireman hats with the built-in siren and flashing light. Thems is loud!
Furbies. They have no off button, they just 'time out' after a while and sit there very quiet, evilly quiet, waiting, waiting for a sound to trigger them. If you happen to bump them or make the a clapping sound (even television clapping) they go berserk and you can't pull the batteries out without finding a screwdriver first. I have subsequently been told, by a particular recipient, that a vat of acid does tend to quieten them down.
These are really hard to find, but in some joke shops you can find this real gross looking fake hand/arm combo. While not strictly 'given' as a gift, when invited to a party, I do like to leave it behind in the fridge as a 'gift' and when the sound sensor is activated (say opening the fridge at 2:00am) it just flops around.
The singing fish. I can't remember name, but it's something like Billy the Bass or something just as asinine. I like to 'operate' on the fish first to ensure that the on/off switch is permanently in the 'on' position and then glue the battery compartment shut. At least until the batteries die, I know that the recipient is truly enjoying my gift. I then get very distressed the next time I go over and Billy is not proudly on display as though ... what you don't like my gifts?