Na-adjective (keiyodoshi), Noun which may take the genitive case particle 'no', Noun
following a single pattern; conforming to the same pattern; one-track; single-track; repetitive; predictable; stereotyped
居酒屋で飲んで、カラオケか。俺達もワンパターンだな。We're doing the same old routine: going bar hopping and then to karaoke.
Also written ワン・パターン、ワンパタン