ha-HAAAAH! "English as she is spoke", methinks!!!!
the phrase 'a bit dead' bears direct comparison to the words put in front of that other word - UNIQUE.
People say:
VERY unique
TOTALLY unique
SOMEWHAT unique
MORE unique
LESS unique etc etc
and none of these things are possible as there are not degrees of uniqueness.
Something is either unique - or it isn't.
Something is either dead, or it isn't.
However it is much more usual to say 'Oo er, me leg's gone a bit dead' rather than 'I have recently been sitting on my foot for a period of about half an hour's duration, which has unfortunately rendered that same lower limb somewhat numb' - isn't it?
Jen