That's just bros being bros, that's how they behave with each other.
And Charlie Brown CAN be kind of pathetic. Have you never had a friend that's down on himself a lot? You eventually learn to kind of get in on the fun and dig at him a little. But it's all in stride and you're still friends.
Linus and Charlie Brown are bros.
And, fuck, Linus is kind of a loser too. I feel like adult readers love his philosophy and theology talk so much that they forget it must be fucking insufferable to the other kids. AND he drags a security blanket around. Linus is a loser too, but Charlie Brown sticks by him, no matter what.