I've just become one expression smarter!
The expression is 'pet peeve'.
Here are some definitions:
Main Entry: pet peeve
: a frequent subject of complaint
The Free Dictionary:
A pet peeve is a minor annoyance that can instill extreme frustration in an individual. Typically each person has several pet peeves that aggravate him more than the average person. Another person may not react as negatively or at all to the same circumstance.
But there's more! (More?!)
This website offers an extensive list of pet peeves.
(this useless info was brought to you by DeCecco enterprises LtD)