For my HK friend HL: Crack is a lower grade of cocaine.
So my friend A likes to use the word "crack" a lot. A person who's being a moron : he/she is smoking crack.
A dish that's so delicious that we can't stop eating: It has crack inside. :D
(More) note to HL: When you say something/someone "cracks me up" = so funny it makes me laugh. :D