This is a repugnant unconscious field set up in a 30 meter radius around the mutant. Any organic being friend or otherwise, will have a 20% chance of wanting to attack the mutant upon first entering the field, otherwise they will be as rude, unpleasant and downright obnoxious to the mutant as they think they can get away with.
Luckily robots and computers are unaffected by the field, although this could be changed (GM discretion) if the player is lucky to generate the Hostility field mutation twice or gains it again later during play.
The player should be encouraged to play up whatever they think causes the hostility as well by being as disruptive and annoying as possible during game sessions, and if this is done well it is recommended that the GM rewards this when the player soon has to generate a new character.
This power should not be allowed for players who view the game as 'hack and slash', as they will use the mutation as a license for murder sprees and XP generation.