It's not an anti-proton, but there is a particle that has the potential of "destroying" the universe.  I forget what it was but the reason it could "destroy" the universe is that if it collided with a regular particle, it would result in the regular particle releasing some energy and getting converted to this special kind of particle, two particles then knock into 2 more particles and convert them and so on and so forth until the entire universe is screwed. 
The reason for this had something to do with the special particle inducing a more stable state.  Apparently these particles are generated regularly in high energy experiments but since they are created in particle-antiparticle pairs they annihilate each other before doing any damage.
In any event, I'm sorry if this post makes little sense or isn't accurate, this was something that my Quantum Mech. prof mentioned last semester and I didn't quite understand how it works.  In any event, he said they calculated the probability of destroying the Universe on every high energy collision at something ridiculously small, of the order of 10^(-40) or something along those lines.  I'll see if I can dig up some more information about this.