when someone happens to fall in love with a girl who had been before perceived as a nerd. usually ends in the singing of a song.
Boy 1: That girl is such a nerd.
Boy 2: No she's not, she's really cool.
Boy 1: Oh, no.
Boy 2: What?
Boy 1: You must have Granger Danger
Boy 2: I think I feel a song coming on.
When a girl shows up to a big event, often a dance, and is suddenly noticed as beautiful by her peers and/or love interest(s). Most of the time, she wears a pretty dress, lets her hair down, and takes off her glasses, and this is all that must be done.
When Shelly showed up to the dance in her new strapless, it was total granger danger.