Irritating person beginning to become more frivolous (8)
I believe the answer is:
blighter
'irritating person' is the definition.
(I've seen this before)
'beginning to become more frivolous' is the wordplay.
I cannot quite understand how this works, but
'frivolous' could be 'light' (light can mean trivial or unimportant) and 'light' is found within the answer.
The remaining letters 'ber' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for blighter that I've seen before include "Villain" , "irritating person" , "Pestilential fellow" , "(Wretched) fellow" , "irritating guy" .)