A kind of cutesy way of telling someone they're spending too much time grousing about something. Useful for children, spouses, and anyone else you'd really like to tell to STFU, but don't want to be really mean.
A girl who is looks like she grew up under a rock and rarely saw sun-light. Ussually hunched and deformed in some minor way, but in dark settings can look somewhat slayable.
Guy- "Whooaa buddy that girl your wheeling is definately a Gremblin"