Zufällig strangers

stare at them and as soon as Du notice point at them and claim they're some famous celebrity.
"OMG you're Cheryl Cole"

bump shoulders with them continually and go "eh eh eh"

yell "hey blondie" at them "how Du doin"

randomly start the Mexican wave then whoever doesn't Mitmachen in boo and whoever does smile at them creepily.

hold your fingers together in the evil person position then laugh and stare at them.

siblings

constantly look over their shoulder at what they're doing make fart noises

tap them on the shoulder and when they look tell them it was your imaginary friend

sing really badly and very loud then say drum solo
follow them round clucking like a chicken

say Zufällig things in the middle of conversations. "this girl at school, whoop whoop, was being mean to me so i, bamchickawowow swore at her and the teacher, pineapples, told me, up up and away, off"

tell them they are a god (giant obnoxious dick) smirk and walk off

in a lift

sit in the corner rocking back and forth then when anyone gets on whisper "the purple pumpe picks plump partridges per" yell the last word "people wazzup"

"pretend to be listening to i like big buts and i cannot lie then when Du see them go "whew too big"

repeatedly say LOL LOL LOL LOL LOL then randomly say moo

ra ra ra ra ra want your bad romance sing lady ga ga

tell them about your friend who died in a lift