"No, that was not cool."
Translation:Nei, det var ikke kult.
I see this hasn't been answered yet. To use kul as an example for the adjectival endings: kul agrees with masculine and feminine nouns, kult with neuter nouns, and kule with plurals. In this case, kult modifies det, which is technically neuter, hence the neuter form.
However, when it's being used to modify a definite noun, the adjective always takes the form ending in -e: Hun er en kul lærer (indefinite), BUT hun er den kuleste læreren (definite).