When a person, preferably named Meg, does something extraordinary, derranged, or comedic.
Meg: It's 3:42 in the morning where is everyone
Bernard: Yeah that's a Meg Moment
a situation in which you are treated like the unpopular character Meg from Seth MacFarlane's Family Guy.
Lili: I said, "Wouldn't it be cool if Joseph could come to New York with us" and my mom was like "That would be awesome! Let's take him instead your sister."
Joseph: Haha, what a Meg moment.