go a number 2 or 3 mate. you don't need to jump straight into a full razor shaved head. to be honest i prefer a clippered cut (no guard) rather than a razor shaved head. (personal preference guys, don't get angry

) You still have plenty of hair by the look of it so a shave to a 2 or 3 will look tops! that easy!
p.s friends like to rip on each other, its just how it is. i bet you have a red haired friend you've called ranga or red nut for years and you didn't think twice about it, i know i have. its the same, your friends will tease you but they won't mean anything harsh by it, its all about how to percieve and take it on board, just turn it into a joke with them - like "your mum seemed to enjoy it last night" or something

go shave now bro