Phrase commonly yelled whilst charging toward a body of water. It is both a dare and an encouragement.
NORMAL practice would be to turn up at afore mentioned body of water - dam, creek, beach, river - with a group of friends (mixed). Then as you run towards the water stripping bits of clothing off, scream the phrase. This lets you hit the water first being able to have dived under, come up and be in time to turn and watch the others as they struggle to join you.
Once in NEVER tell them how cold it truly is.