an orgasm caused by an excessive amount of surprise or excitement
When Katie saw the Taylor Lautner in the New Moon trailer, she was so excited she had an omfgasm.
John was watching The Empire Strikes Back and when Darth Vader said he was Luke Skywalker's father, John must've had an omfgasm he was so shocked.
Used to express overwhelming excitement, pleasure or attraction.
"dude, check out that bentley!"
"i saw her naked ahah ahahahah hahha hot. hot hot hot hot hto hothtohtoh okay she was in her underwear but still omfgasm"