Slang term for a English policeman, used due to their Tit-shaped hats
"Oi Nippleheed, have you seen Babe, it's about a talking pig!"
"Ow, please stop hitting me with your nightstick you Nippleheed!!"
A nipplehead is a scrawny, drug-dealer looking man (often black) with drooping jackets and sagging pants. They are referred to as nippleheads because of their toboggan, which is hanging loosely off the head, creating a raised point, causing their head to look like a nipple.
Sue: Did you see those guys yelling outside the ABC store?
Alice: Yeah, nippleheads are pretty annoying.
Raised red bump (minus puss) on the forehead acquired from attempting to pop a forming pimple. Failed attempt looks like a nipple on the forehead.
Check out that nipplehead.