Gym class skipped by more irritating sportsperson (5)
I believe the answer is:
skier
'sportsperson' is the definition.
(I know that skier is a type of sportsperson)
'gym class skipped by more irritating' is the wordplay.
'gym class' becomes 'pe' (abbreviation for physical education).
'skipped by' indicates named letters should be taken away.
'more irritating' becomes 'peskier' (pesky means irritating).
'peskier' with 'pe' removed is 'SKIER'.
(Other definitions for skier that I've seen before include "One on the piste" , "needs catching on way down" , "He glides across snow for fun" , "Sportsman who glides over snow" , "Winter sports athlete" .)