When you feel fat, bloated, pimply, ugly and just generally unattractive. A feeling that can sometimes be brought on by eating junk food, especially if other people are watching. Also that grotty feeling at the end of a night out when your makeup is all smudged and your hair looks like crap.
"I'm feeling a bit Britney"
"I don't feel like going out tonight, it's all gone a bit Britney"
"I think I should go home now, before the lights come on and people can see me properly, I'm looking a bit Britney."