From Longman Dictionary of Contemporary Englishdissdiss, dis /dɪs/ verb [transitive] informal UNKINDto say unkind things about someone you know→ See Verb table
Examples from the Corpus
diss• Politicians are always dissing football supporters.• Were all his posse pals going to diss him once word got out?• Just don't diss my little brother, OK?• If you want to diss us, you got to cut it loose. 