Voss is a pretty skinny, reasonably non-threatening looking dude:
hence the “body frame bulimic” description (comparing his thin physique to that of someone with bulimia). He realizes that his previous threat of catching “assault and battery” may be hard to believe due to his appearance, but assures the listener that he was raised to remain true to his word, and will indeed break their kneecaps if they touch anyone he loves.