Irresponsible sort? Bat perhaps (3-2-5)
I believe the answer is:
fly-by-night
'irresponsible' is the definition.
(thesaurus)
'sort? bat perhaps' is the wordplay.
I cannot really see how this works, but
'bat' could be 'night' (I have seen 'Black bat' mean 'night' so perhaps 'bat' could also mean 'night') and 'night' is found within the answer.
The remaining letters 'flyby' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for fly-by-night that I've seen before include "Transitory" , "Untrustworthy person, likely to abscond" , "Unreliable (in business)" , "Unreliable, untrustworthy" , "Unreliable - person who departs secretly to avoid debts" .)