When someone wants to ask someone out, you put "the balls in the pants". Mostly used for girls who want to ask out a guy. Can also be used for a guy who has been longing for a girl for a long time but doesn't have the balls to confess.
Variations can be just saying the phrase, or putting super balls in each pocket to give you courage.
Jocelyn: I really really really like him but I can't tell him. What if he says no? What should I do.
Jasmine: I think it's time for you to put the balls in the pants.