One that springs to mind CBB-wise is Julie Goodyear! 'Nanna Julie' was extremely popular and a 'national treasure' when she walked in - she was rumbled by a Nolan and came out as a bitter, manipulating old has-been. Vile. That banana scene - *vom*
CiviBB - yes Wolfy is the one that instantly springs to mind but there are probably far too many to remember. I seem to remember Tracey BB8 with the pink hair (deal wiv it!), as well as Laura BB8 (in the dressing gown) being culprits. And Lisa BB10 - she thought she'd be the first Mohawk-headed brummie lesbian to clinch the title and was genuinely shocked when she was (quite rightly) booted out.
I think Nikki BB7 is kinda guilty of this too - although arguably she picked things up again after the series ended. When Nikki re-entered the house after initially being evicted she thought of herself on the brink of superstardom, loved by millions, her own tv show in the pipeline - she'd waltz in, fall in love with Pete, win and grace the magazine covers for ever more - truth was, she was stuck up, irritating and 10 times more insufferable than her first stint! Her face when she was first out on finale will stay with me for EVER. It was hilarious.
Also Bubble BB2 - totally shocked that he'd been booted so early - his face told a 1000 stories - the main one being of a man who thought he'd walk into the final being booted within the first 3 weeks. Very satisfying.
I rant, I shall stop :P