Somebody’s pet peeve
Definition 1 of 1
Pro Tip 1/3Subjective Nature
The annoyance varies greatly from person to person; what irritates one might not bother another. 
Chewing loudly may not affect you, but it's my pet peeve.
Pro Tip 2/3Not Universal
'Somebody's pet peeve' often applies to minor, trivial matters, not serious problems. 
My pet peeve is people not refilling the ice tray.
Pro Tip 3/3Colloquial Use
Used in informal conversation, usually not in formal writing or speeches. 
She casually mentioned that her pet peeve is improper grammar.