Annihilate ...

(this animation takes some time to download, one picture at the time...)

In order for particles to annihilate they have to be of the 'same kind'. This has to do with conservation laws such as conservation of baryon number. An antiproton has a baryon number of -1, while the proton has +1. If they annihilate each other the total baryon-number does not change, nor the total charge in the universe. Processes were one of the conserved properties (charge, baryon number, lepton number, isospin, 'charm', etc.) would be violated are strongly suppressed. This means that e.g. that an electron and a antiproton cannot annihilate each other because this would violate both lepton and baryon number and charge conservation (and some others).

The blast you see in the animation above is of course 'slightly' exaggerated...
When an electron and positron meet at low velocity, they are transformed into 2 gamma ray photons of 511 keV energy each. That does not fry you really. It is a whole different situation if we would have 1 kg of antimatter. Convert 1 kg into energy and be prepared for some serious redecorating.  Fortunately, it is practically impossible to make 1 kg of antimatter. It has been calculated that all the antimatter produced so far over 40 years is barely enough to heat up a cup of coffee!. The efficiency of producing antimatter is extremely low. As a result it is much too difficult and expensive to generate 'useful' amounts of antimatter. This means that any science fiction fantasies about antimatter propulsion are really just that: fantasies...

It might be enlightening to read first this nice page on antimatter as energy source which is part of the home page of the PS210 experiment producing the first antihydrogen, and then this one dealing with antimatter propulsion. We leave the conclusions to you ...