Bad person about to be given notice (3)
I believe the answer is:
cad
'bad person' is the definition.
(cad can mean a dishonourable person)
'about to be given notice' is the wordplay.
'about' becomes 'c' (abbreviation for circa).
'to be given' means one lot of letters go next to another.
'notice' becomes 'ad' (both can mean an advertisement).
'c'+'ad'='CAD'
(Other definitions for cad that I've seen before include "Dishonourable man of decadent sort" , "A knave, real rotter" , "Bounder, scoundrel" , "A rotter, by Jove" , "he's no gent" .)