Quoted from a recent comment in another group:
"A F--- is Someone who THINKS they know something about food and the science of cooking."
I've seen this grammatical construct (singular to plural) often enough to know it's, at the very least, not uncommon. I searched the net, but unfortunately I've been unable to determine wether English grammar allows it or not - I guess it doesn't. Is it indeed correct? Or common, or accepted?