(Sorry if my formatting is bad I'm on mobile)

I have a friend with very mild bipolar disorder who is mad at me over a school shooting joke her friend told us. 

I have the very stereotypical school shooter look (A.K.A I'm A white kid who wears a trench coat, combat boots, ski mask, and snap back.) I'm very use to being the butt of the jokes in my school and she's use to hearing them. Well one day she joked around saying that if I where to ever go through with the jokes I should give her my hat first. Well she walked away for a bit and her and my close friend suggested I should walk into school one day put the hat on her head and say "I won't be needing this anymore". At that point I started cracking up so she came back over and asked what was funny, so her friend repeats the joke and she gets mad and storms off. She slowly distanced herself from me but not the people making the jokes. She's also been trying to ruin my life by grasping at straws to go tell the school officials. I finally asked one of her friends why she's been doing this and they brushed it off as her bipolar disorder (we where friends for 6 years and this never once came up between me and her.) I finally got tired of this and started retaliating by making fun of her for every insult thrown my way

Her friends started confronting me calling me the asshole for "bullying" a girl with "bipolar disorder". They also have been distancing from me or getting mad when I insult her back. The friend who made the original comment refuses to take the blame because "it's funny to see me mad". 

I'm not looking for justification for me I just want to get other people's opinion on whose the asshole. I'm also sorry if it seems like there's a lot of bias I tryed my best to stay subjective