I am fluoroantimonic acid. I actually dissolve you, as I am a far stronger acid.

The next user is explosively dissolved by me, as fluoroantimonic acid explodes on contact with water. 

I'm not water??? I'm a fluoroantimonic acid too!

The next user eats me and dies of poison.

I am poison too.

The next user is a human who eats me.

lol. once again I taste the acidity of you before actually eating you.

The next user uses a cyanide pill on themself

Fortunately, it was filled with sodium ferrocyanide, which is not especially toxic, so nothing happened.

I collide with the next user at 99.999% of the speed of light.

You are a subatomic particle. You have the velocity of about a baseball. I have a nasty bruise :(

The next user is him, who was absorbed into my body.

I am a dark matter particle and pass through you harmlessly :)

The next user drinks a bose einstein condensate.

I am a alien, and am immune to poisonings, 

The next user vomits so hard his eye balls drop out

I'm blind, but still alive.

the next user is infected by a zombie. While there is no cure.

I make a cure.....

The next user dies. With no way of revival.

Cause of death: unknown...