Is it normal for a friend to treat me like this?

So I have this "friend" who keeps claiming that he's my best friend, but he treats me like crap.

Here's a bit of a rundown. I'm not the most popular person at school, but nobody really dislikes me either, only because I don't really know anybody very well. However, he claims that he's my only friend, and that nobody else likes me at all, and I'm lucky to have him around. He on the other hand, claims that he's popular, yet he still hangs around me all the time for some reason. He only started hanging around me when his other friend stopped hanging around him.

Also, he continually insults me, saying I'm a weirdo and a strange person and that's why nobody likes me. When I call him out for it, he says he's only joking, and that he calls his other friend a "fatass" all the time, but I think there's a difference when you tease about someones weight compared to attacking someone's personality.

I do have other friends, but they just don't go to the same high school as us. When I talk about them, he always says they're "weirdos because they hang out with you" or they're not really my friends. One of them whom I consider my best friend, is probably one of the most "normal" and outgoing people I know, whom doesn't do or say anything at all to me that I would consider insulting.

And if that doesn't convince you, every now and again he might say something like "I thought you were just misunderstood, but no, I see now why nobody wants to be friends with you." Then I ask "Then why do you hang out with me then?" and he replies "Because I want to help you." And he passes off everything he says as constructive criticism.

On the other hand, there are times where he's completely nice and polite. It's weird, like one day he's respectful, and the next he decides to be all rude and douchey.

Do "friends" normally do this? I personally don't think its normal, I just want to hear other people's input.