I was in a special containment unit that is oblivious to explosions

the next user just swallowed a lot of mentos and coca cola

It seems that you're insane and mistakes a regular cactus for a cactuse with a mouth. In other words you picked the wrong cactus.

You ate an Iphone and is now clogging your airway and your mouth is too small to force it back out.

apples taste good, i swallow it.

the next user dies from a glitched time portal, causing them to infinitely circle time forever.

But time may or may not be infinite, as time may be a finite construct. Your circle breaks because time is derpy.

I now push the next user into a black hole, making them into a spaghetti mess.

I managed to avoid spaghettification in two ways. First, I happen to be a gamma ray photon. Second, I get stuck at the black hole's inner horizon, because the force of gravity actually reverses further inwards.

I poisoned the next user with deadly dimethylcadmium vapors.

Well, I was in Bejing, but your target area was Moscow, so the russians accused you of mass poisoning.

Next user is having a 50,000 volt, 508 ampere voltage straight accross your heart.
You have NO SUPERPOWERS, NO SUITS, NO INBUILT COMPUTERS, NO IMPLANTS, NO NOTHING, and you are 3 years old.

I am a three year old tree. 

I now forcefully feed the next person osmium tetraoxide

I am a plant. My fruit ripened really fast.

Next user Gets eaten by antimatter. If he survives that, he gets burned alive, decomposed to dust, goes through a black hole. No chuck norris. 

~BUT I AM DARK MATTER~

I turn into a singularity and consume the universe