To describe how you react when you see something of extreme coolness. Taken from the condition that dogs get called rabies, when foam starts coming from their mouth. Instead, this is what occurs when a person drools and it forms into a white, bubbly foam, especially after they see something cool, new or desirable. Although this is rarely seen, and this is probably a good thing, the term 'froth' is still used to describe how people react when they are faced with something that they want.
"Dude, have you seen Joey's new car?"
"Oh yeah, man! I froth over it!"
"Stop frothing over that new TV show, buddy"
"Janie from Class 12-B makes me froth"