You get burned by fire.
I insert Coops' burnt skull.

You get killed by the devil, who is angry since he couldn't carry out his own revenge.
I punch the vending machine.

The vending machine punches you.
I insert a netbook.

The machine eats it for breakfast, then spits out its keyboard.
I insert my hand.

You get a prosthetic hand.

I insert an arm and a leg.

The machine, tired of causing harm and murder, decides to gently place a monkey's paw into your hand, and then spit your hand back out.
I put in one of lafe's mods.
Edit: Damn it MLC, it didn't even tell me you posted.

The machine commits suicide.
I insert a ZD bomb.

i press the eject key
i insert a zombot

The machine ejects some shredded remains and a head.
I insert a vending machine.

You struggle and sigh, sad that you're not quite powerful enough to force a vending machine into a 3mmX1cm coin slot.
I put a quarter on a string in the vending machine.

You get your money back, plus your snack/soda of choice.
Insert a dollar with a string on it.

You get a Moderator (hero class) with a watchful eye on this thread.

I insert the perseid meteor shower.

It eats your money, the string breaks, and it gives you plain M&Ms instead of Peanut.
Insert bullets into slot, via shotgun.

EDIT: SERAPH NINJA.

I suppose now that this has a Moderator Hero on the watch it's ok to participate in.

You get a shotgun shell box back, empty.
I insert a sandwich.

The machine makes Duh make me a sammich.
I insert crumbs left over from said sammich.