usually the scare test works awesomely well.

just wait untill your buddy is relaxed. then, suddenly jump out at them! if their reaction is late/sucks, than they are stoned. my friend did it to me 4 times going up my stairs, each time i fucking fell over. i even knew the shit was coming, and i still fell over XD. animals will also seem to be crazy/wild. whenever im baked my dog seems to be moving at the speed of light.

or you could think your in space, laughing at twirling xmas trees (see my post in experiences).