Having done some physics, I feel I must point out a couple of things! A black hole is basically a lump of matter so dense that even light will not escape its gravitational well before it hits the surface (if there is one). When a black hole is created, you still have exactly the same mass but squashed into an incredibly small space. When you're talking about making a black hole with only a couple of elementry particles, the event horizon (the point of no return for light) would be so small that the chances of any light interacting with said black hole are equally as small.
If you're worried about the black hole hitting other particles, first of all, you will be using a huge particle accelerator - these things are filled with a vacumn. The only particles you get in there are the ones you put in.

Looking at it from a maths point of view:
G = 6.67259 * 10-11 N m2 kg-2 - the gravitational constant
m = 1.672 52x10-27 kg - mass of a proton
c = 3x108 m/s - the speed of light

the event horizon has a radius r of:
r = 2 G m/c2
r = 2 x (6.67259 * 10-11) * (1.672 52x10-27) / (9x1016)
r = 2.48000893929x10-54 m

Pretty small!

The time it would take such a black hole to evaporate (via Hawking Radiation) would be:
tau = c2/(3 K) mu3

K = 3.563x1032 - K is is related to sigma and thus the luminosity of the black hole, the surface area and temperature.
mu = 1.672 52x10-27 m - the initial mass of the black hole which is the mass of a proton.

tau = 9x1016 /(3 x 3.563x1032) x 4.678x10-81
tau =4.1813902213747281232309388314513x10-97 seconds

This is not really enough time to do any serious anihilating!

Thanks to Blush Response for pointing some things out and spotting some mistakes!

http://www.alcyone.com/max/writing/essays/black-hole-evaporation.html - some equations for black holes.