I'll start this off:

I had a dwarf sorceror with a rtg 5 animate spell.
An NPC was giving the troll in the party a hard time, since he was a "nobody", we decided to play with him.
I animated his chair, had it grab him and walk him out, where we hailed cabs till we got one driven by an ork. Handed the driver 500 nuyen and let him know the human didn't like orks.

Haven't actually done this (yet!), but I just picked up a Force 7 Influence. One of these days, I'll slap someone with "From now on, when I snap my fingers, you will cluck like a chicken...".

*shudder*

Actually, the funniest and stupidest thing I've ever seen was a shaman casting hot potato on a panicked rigger to get him to stop the car.

Unfortunately for the shaman, I was a Fenrir shaman (beserker when injured) in the car with him, and the resulting crash injured me. I killed the shaman (had no choice) with a point blank flechette burst from my Viper slivergun in 1 turn. Granted, I healed him as soon as I had recovered, but still...ingenious use of the hot potato spell.

I always thought it would be fun to use Mob Mind to pull a stunt like Jim Carrey did in "The Mask."

"They call me Cuban Pete
I am the king of the rumba beat!"

Shaman in ongoing campaign did the following:

Used Levitate to pick up an unconcious Barghest and proceeded to wack a ganger with it's limp body while on the astral screaming, "Taste dog butt!"

Please do not blame me for the deluded actions of others. Only my own.

had a mage that loved the Transform spell (this was in SR2 days)...

he would transform enemies into carp and sustain it until they passed out from not being able to breath with their gills...

...one time they were doing an extraction, where the sarariman wasn't supposed to get injured - they transformed him into a turtle and passed him around like a football to get past the guards - since the sarariman's normal reaction to all this was to curl up into a fetal ball, he retracted inside his shell - eventually they threw the turtle out the window to be caught below by the rigger, who then put him into the back of their van - the mage could then drop the spell, and the runners were free to engage the guards and escape without worry of their client getting injured.

In my last campaign I had a Mage who took the Animate spell and the Demolitions skill at chargen. His thought being self propelled balls of c-12 doom .
So during the campaign the team got the job of killing as many Triads at a particular meeting as they could. Solution, go to local art dealer and buy three ceramic bird sculptures(hollow), fill them with c-12 and ball bearings, animate birds, shoot out the windows, deploy flying claymore mines.
Triads are still cleaning the blood off of the walls.

My group's mage likes to use Influence a lot for humorous effects. He started a brawl once between some guards when he had one guard pinch another guard's ass (both males). The runners slipped in pass the security who were duking it out on the floor.

We were in stitches when two of the PCs got drunk after a meet in a fancy club and asked our shamen to cast invisibility on them. She didnt :E Thinking they were invisible they then went potty trying to cause all sorts of trouble. Eventually being thrown out into the gutter nakid (who can see?).