"Chalk It Down" is generally used by stoners in Ireland, it can mean various things, too many to even list but people use it as a substitute for "chill" or "ok" or "in your face"
Example 1:
Girlfriend: Are you messing around with Lisa???!!!
Boyfriend: Whoah Chalk it down! (chill)
Example 2:
Boy1:You coming to the party tonight?
Boy2:Ya, i'll be there @ 9, chalk it down! (ok)
Example 3:
Boy:I fucked your 'ol doll last night, ha chalk it down! (in your face)
12 step recovery jargon referring to someone new who talks about how great life is, now that they'resober. Usually meaning that the person is out of touch with reality.
The new guy seems pretty happy for a dude who has no job, no money and no family. He must be on a pink cloud.