1) Expresses utmost concurrence/approval with what your bredrins are saying;
2) Damn straight;
3) You know that/ you know that mother fucking shit;
4) thems the breaks i.e that is just the way it is/ consignment to a sad state of affairs.
Also can be used long form "and aint the the mother fucking truth" or abbreviated to form "ATTMFT"
"I feel to get drunk tonight"
"Ain't that the mother fucking truth"