Surely if someone is slagging you for being bald they are already acting like a 14 year old.
Back in the days before I was losing hair myself, my boss at my old job had recently survived cancer and lost his hair due to the treatments. This old guy I worked with leaned over and said "Look at him. He looks like a penis with ears."
The guy had f*****g cancer and he was not safe from bald shaming.