it seems min so i wouldnt worry about him, its a shame about his age and your at 15-up your bodies start to produce hormones which kinda ct like steroids, so he could be stronger than you
i would not suggest trying to attack him, get him to back off
its just a minor thing and i wouldnt worry to much, as for your friends and the bully calling you names such as The Elephant Man, give em a hit or something, nothing to hurt them it just tells them to stop.
my name is Will and im 16 and just to piss me off half my friends call me Wildo (as in dildo) , but i know its all fun and games so do they, i give em a wack every time but nothing hard or could hurt.
best of luck and i hope it gets sorted, name calling shouldnt be a big issue, just laugh at it. hell when i was bullied i used to find the names they called me funny and the venonm they used even more funny (venom as in the hate in their voice) and id laugh my head off, it used to piss them off cause it had the opposite effect.
just laugh names off, as for our friends they aint bad there just laughing around abit, it happen, there not bad friends
i hope this gets sorted without booting your friends away