Be not the done thing British old-fashioned phrase informal
Used to refer to a behavior or way of doing something that is not suitable or socially acceptable.
Smoking in the hospital or school is not the done thing.
For your information, spitting in public is not the done thing.
In those days in Asian countries, having higher education was not the done thing for girls.
The verb "be" should be conjugated according to its tense.
Extremely ugly; unlovely; unattractive
I hate frogs because they’re as ugly as sin.