・・・、。
...There's plenty I'd like to say, but butting in here would be tacky.
Literal
...Want-to-say thing [topic-は] various-ly exist-[but-のだが], here [locative-で] mouth [object-を] insert [nominalizer-の] [topic-は] uncouth [quotative-という] thing.
野暮 (やぼ) is a rich cultural word — it means 'tactless, boorish, lacking refinement or delicacy', originally the opposite of 粋 (いき, urbane sophistication) in Edo-period aesthetics. The idiom 口を挟む ('insert one's mouth') means 'to butt in, interject'. The ending ~というもの is a way of asserting a category judgment — 'that's what you'd call uncouth'. のだが is the formal/written ~んだけど.