Some devil erupts, getting more unpleasant (5)
![Ross](/clue/static/ross-mug.min.png)
I believe the answer is:
viler
'more unpleasant' is the definition.
('vile' can be a synonym of 'unpleasant')
'some devil erupts getting' is the wordplay.
'some' indicates a hidden word (some of the parts of the word are used).
'VILER' is hidden within 'devil erupts getting'.
(Other definitions for viler that I've seen before include "...more diabolical" , "More nasty" , "More reprehensible" , "Liver (anag.)" .)