DA is an abbreviation for the expression "dry as", not meant literally but meaning that something is particularly bad. I believe it derives from someone originally going to a party. We would say a bad party, without much booze to be dry or in this case..."dry as" or indeed "DA".
This should be pronounced as the individual letters, e.g. Dee Ay.
example 1: We went to the party and allowed it because it was DA.
example 2: I went to see that new movie at the cinema but it was DA.