Well there's no certainty she'll think it was from the guy she likes, but yeah I know, I did a bad thing, but it was all for the lolz right?

It still doesn't seem right. If your friend doesn't like her, than he just doesn't. The truth of the matter is that doesn't really change. Now she thinks that he likes her, and so she's more inclined to keep pestering him even though he's not interested. Basically, you've made your friend need to spell it out to this girl that he's not interested. That's never fun, but I suppose he should've done that anyways. Whatever.

I'm not trying to justify myself, because I'm obviously in the wrong no matter what turn of the story, but she's got to be happy now. It's not like it would really upset her too much when she finds out her assumption is wrong (the assumption being that the guy she likes, likes her back), because she'll still know someone else has a secret crush on her and I don't know, -blam!- it, maybe I'll tell her I sent her the flowers.