In Tabula Rasa, after the memory loss Buffy had no idea who she was and decided to call herself Joan. Why is that funny? what am I missing?

It's funny because Buffy depics a "woman warrior" and when she chose the name Joan, it was a coincidence that Joan was the name of the woman warrior accused of being a heratic. "Joan of Arc".

I think because it's a rather lame name (for a superhero I mean) and it's not really for young people - no offense to anyone named Joan :)

I dont think its funny

Well, it's just the oddity of it. Buffy is a very modern name and Joan isn't, and it evokes Joan of Arc.

I don't really think it's all that funny.
I think it's just because Buffy is just very unusual and you would expect a VAMPIRE SLAYER to have a name like that.
Then all of a sudden BAM! She has a lame name like Joan- absolutely no offense to anyone called Joan, I LOVE the name Joan, I just mean compared to Buffy, it seems plain while she's still like the hero with a plain name.
That's really all I think it is.

As well as Joan being a bit plain for someone who's name is Buffy and a superhero but it's also very random and completely different to Buffy.

I don't think it's very funny, but i guess it kind of is because Buffy is a unique name - i haven't met or heard anyone so far who is actually called Buffy. And Joan is a name that most people have as thier name. Plus it's not really a superhero name either.

Well, Buffy is an awesome name. Joan is not. Its a matter of Lameness and Coolness :D