blunder

Long, hot soaks in winter are a classic faux pas , since exposure to extreme heat after having been in the cold can cause small visible blood vessels to appear at the skin's surface.

— Elle

especially : a socially awkward or improper act or remark Audiences must be supportive and enthusiastic—lots of clapping, no heckling. (And talking on cellphones during the performance is a huge faux pas ).

— Claudine Ise

a significant or embarrassing error or mistake