The only thing that aggravates me about these stories is the part where is says "Southwest later apologized". In many cases the passenger IS clearly too fat or being a tool and is rightfully removed. It just demonstrates a complete lack of backing and undermines the front line employee who had to make that call. Is it just the policy that in these cases an apology is given to appease the ousted passenger?
Well, in this case, he wasn't fat. He argued with the flight attendant and cursed, which while the door is still open is easy prey for a "thanks for playing, you're outta here..." action.
Maybe she saw it as him being clear he wasn't interested in "following crewmember instructions",
More likely, his saggy drawers presented a real hazard during an evacuation (how exactly does one manage to exit quickly with a waistband hanging below their hips?....)
Who knows, because we rarely hear the other side of the story.