Well, the expression above is even new to me as an Arab!
In my dialect though we would say such expression not for being cold, but for not being done well (i.e. the coffee has more water and doesn't taste good).
In MSA 9ahwatuka/ki is a "moubtada2" and must be in the nominative case. Such alternatives like 9ahwatak for a male and 9ahwatik for a female are Egyptian accents which don't make any sense in Standard Arabic