"Down the Beach" is a phrase originating from California surf culture, used to define someone who is a kook, generally meaning that they should beat it and go surf down the beach. In context, it is often shouted indirectly, as a statement to your friends or other surfers indicating there are kooks in the water. Hopefully the kooks hear you and get the message. On occasion it is shouted directly at the person, which basically means beat it and go surf somewhere else.
ex. 1: "Down the Beach!" (or just DTB)

ex. 2: "Oh shit, check out who's paddling out; Down the Beach!"

ex. 3: That guy is so down the beach (often abbreviated as DTB).

ex 4: "Yeah, check out this guy - DOWN THE BEACH!"

ex 5: "Fuckin' beat it kook, Down the Beach"
by A K Jackson November 3, 2007
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Engaging in an extremely slow process.
Maurice was undertaking the challenge of counting all the hairs on his body. I told him he might as well be kicking dead whales down the beach.
by Edward Marshall Shenk July 11, 2006
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When a person has messed up and run away

or

when a person has mentally checked out of a situation
She/ He has sent out an email to all of the wrong people,

Oh my god, she's/He's gone down the beach.
by Lickytoads June 21, 2017
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down the beach = lets go to the beach

Origin = The Shire (Sutherland shire, Sydney, Australia)
Shire boy 1 text: Lets go down the beach

Shire boy 2 text: Okay I will meet you there in 20 minutes. I am catching the train from Sutherland
by Junkie69420 October 11, 2021
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