OMG

"OMG" was an exclamation which could be used to express surprise.

Upon watching the TARDIS materialise on stage, a man reacted with "OMG, LOL, what's that?". (TV: The Doctor Drops In)

When, on an episode of Meet That Hero!, E.T. grew a Kryptonian singing flower, Supergirl reacted with "OMG, a Kryptonian singing flower!", and voiced her newfound support of starting an "alien club". (WC: Supergirl Meets E.T.)

Behind the scenes
Although not stated in any valid DWU sources, "OMG" was an abbreviation of "Oh My God", "Oh My Goodness", or "Oh My Gosh", which is commonly used in online and digital spaces.