Extremely thin person in bar, a Kenyan (4)
I believe the answer is:
rake
'extremely thin person' is the definition.
(rake can humorously mean a very thin person)
'in bar a kenyan' is the wordplay.
'in' says the answer is hidden in the clue.
'RAKE' can be found hidden inside 'bar a kenyan'.
(Other definitions for rake that I've seen before include "Stage's sloping angle" , "Gardening tool for the dissolute fellow" , "One may see a croupier with one" , "Inclination - dissolute man" , "Garden tool for a dissolute fellow" .)