Quite improper, old boy! An unseemly display (7)
I believe the answer is:
obscene
'quite improper' is the definition.
'obscene' can be an answer for 'improper' (I've seen this before). I am not certain of the 'quite' bit.
'old boy an unseemly display' is the wordplay.
'old boy' becomes 'OB' (abbreviation for a private school 'old boy').
'an unseemly display' becomes 'scene' (I've seen this in another clue).
'ob'+'scene'='OBSCENE'
Can you help me to learn more?
(Other definitions for obscene that I've seen before include "Morally offensive, disgusting" , "offending sensibilities?" , "Highly offensive" , "Indecent or pornographic" , "Pseudonym" .)