not suitable for formal occasions or polite company due to being crude, coarse, or lacking in class

这种粗鲁的行为在正式宴会上是不登大雅之堂的。

not considered elegant or sophisticated enough for formal display or high society, particularly regarding artistic or literary works

这种通俗小说虽然畅销，但常被文学界认为是不登大雅之堂的。