The word gripe, as both noun and verb, refers to a minor complaint. Why gripe about the size of the portions when the food is so awful?
The key to gripe is that as complaints go, it's trivial. You don't gripe about your house burning down or the cost of medical care. You gripe about your friend's status updates and the fact the Yankees have too much money. A gripe can last a while. For example, the city has been hearing gripes about parking rules for a generation, but as complaints go, it's just not getting a lot of traction. One person's gripe, however, can be another person's major headache. It all depends on your point of view.