Finished with pest egghead tends to regard too highly (8)
I believe the answer is:
overrate
'to regard too highly' is the definition.
(I've seen this in another clue)
'finished with pest egghead' is the wordplay.
'finished' becomes 'over' (over can mean finished or ended).
'with' is a charade indicator (letters next to each other).
'pest' becomes 'rat' (rat can mean a nasty person).
'egghead' becomes 'e' (head letter of 'egg').
'over'+'rat'+'e'='OVERRATE'
'tends' acts as a link.
This may not be right. It may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for overrate that I've seen before include "Score excessively" , "Inflate" , "Make too much of" , "Expect too much" , "Misjudge" .)