An Unimportant Human Being Who Is An Energy Vampire To Those Around Them Who Serves Absolutely No Purpose In This World And Feeds Off Any Type Of Negative Emotion Given Off Like The Children Of Satan They Are, Do Not Fall Into Their Friendship Trap Because An Unsuspecting You Could Be The Next Victim Of Their Wrath, STAY AS FAR AWAY AS POSSIBLE FROM THESE FAT MUTATIONS AT ALL TIMES FOR YOUR OWN GOOD AND SAFETY.
Someone that picks on people they thought were uglier inside is no different than someone that picks on people they thought were weaker (physically, mentally, spiritually, or any other measure someone can think of).
The true bully saw the guy calling the girl fat as an easy target because he saw the guy as more of a bully (weaker) than himself, and was quick to take advantage of the situation (since any guy calling a female fat must be a sick, heartless, and pathetic coward).