Buffoonish, irrational boss goes around (6)
I believe the answer is:
stupid
'buffoonish' is the definition.
(thesaurus)
'irrational boss goes around' is the wordplay.
'irrational' becomes 'pi' (an irrational number).
'boss' becomes 'stud' (both can mean a metal decoration).
'goes around' means one lot of letters goes inside another.
'pi' placed inside 'stud' is 'STUPID'.
(Other definitions for stupid that I've seen before include "Dull" , "Idiot" , "potty" , "Idiotic" , "Irresponsible" .)