I roasted my friend's bully using Reddit insults and now my friend is embarrassed

Me and my pal Bob (not his real name) have been besties since the beginning of high school and we enjoy each other's company a lot.

The only problem is Mary (again, not her real name), a big mean bully who's been trying non stop to ruin Bob's life for seemingly no reason other than her own miserable sense of satisfaction.

So, one day, while me and Bob were laughing while browsing r/memes during recess, Mary approached Bob from behind and purposely startled him, almost making him drop his phone to the ground. She bursted into laughter

That's when I decided I had enough. I sent her a gaze that could kill a God himself, and told her: "Oh yea? Well, you remind me of a penny; two faced and not much value". Instead of her tearing up and screaming like I initially thought, she just responded with a dumbfounded expression. So did Bob.

Confused at the way the situation has escalated, I decided to throw another insult that would totally wreck her ego. "If the dumb juice was a thing, it would have been you". Once again, I was met with a completely different reaction and Mary bursted into laughter, louder than before. A few students who were passing by gave me a quick look as if I screwed up or anything. As for Bob, he tried to hide by looking away and covering his face with his palms.

During lunch period, Bob and I argued about the whole thing. He said that I embarrassed him and that he heard some girls giggling and whispering things about him as he was walking down the hallway. Needless to say, since then Mary's constant tormenting towards him has become more intense, more exhausting and more annoying than usual.

Am I at fault here? Personally, I think not but what do y'all think?