The friend in question we will call Tom. Tom has always been kind of homophobic. Specifically the "I'm not a homophobe, but if I see a gay couple I'm going to call the a couple of f-" brand of homophobia.
You might imagine how difficult it was to come out as bi to all my friends, him included. He was suprisingly alright with it, and continued treating me as normal, which was nice. However, a certain meme began to spread around, particularly on Instagram. It was the "Anti-LGBT Emoji"(And yes, I know that to some it means "no homo" but that isnt the case for Tom. The specific memes on Instagram he was liking all referred to it as the "Anti-LGBT Emoji")
I saw him liking these memes on Instagram. I was kind of annoyed at the meme and Instagram as a whole, but all I had to do was close the app and it was gone. This wasnt good enough for Tom though, and he started sending it to our group chat. I had told him to cut it out and made it clear he was getting me mad. Of course, this only made Tom want to do it more. He kept spamming the emoji and eventually I just muted the chat. I was thinking "He's being annoying and purposefully trying to make me angrier, but it's fine. As long as he's dropped it by the time I'm back, I'll let it go."
So then I decided since I came out privately to everyone who mattered to me, I was finally ready to come out in a more public way. I made a profile picture for myself on Facebook with myself in front of the bi pride flag. Uploaded it, and sure enough...
Tom, in the comments, with the Anti-LGBT Emoji on my profile picture that I used to come out publicly. I had enough. I didn't care if it was just some emoji.
You see, I remembered a few monthes ago when Stan Lee passed away. Tom was very upset, and fell into a slump for a while. I did my very best to help him out of this slump, and I remembered him telling me "He was my hero, man. I really wanted to meet him. I wanted to go to cons hoping I'd meet him."
I saw an opportunity to hit Tom where it hurt. I replied to his comment with "Haha! Good one Tom, wanna know whats funnier though?"
"Is it [Emoji]?"
"Nope! That you thought youd actually get to meet Stan Lee before he died!"
and thus followed a long comment chain where he tried to justify his emoji and even some of my friends jumping in trying to convince him to just stop (mind you, this is all public, including to my parents.) 
It ended with me explaining to him that even if it was a joke, everyone has jokes they dont like, even him. He said he would stop doing it, though he didnt apologize.
It has been almost a week since then now, and I've been thinking it over. In my head I think I did something good, but in my heart I think I feel bad. We havent talked since then, and the rest of my friends have started pulling away from him. This situation isnt entirely why theyre pulling away from him, but this was the straw that broke the camels back.