To be overwhelmed by ecstatic joy, a state of ecstasy or rapture. Used online as an action, to show that someone is attracted or interested in someone or something.
She is so hot... Swoon...
Nasty, dirty, disgusting, foul, revolting, yucky.
Are you sure you want to eat that Chinese food? It looks all grody.
In general, fan service refers to scenes designed to excite or titillate the viewer. This can include scantily-clad outfits, cleavage shots, panty shots, nude scenes (shower scenes especially), etc. Some broader definitions also include things like cool mecha, big explosions, battle scenes, etc. Basically, if it has little plot-redeaming value, but makes the viewer sit up and take notice, it's probably fan service in one form or another.
In Evangelion, the episode preview for "Next time, service, service!"