Frown upon
Definition 1 of 1
Pro Tip 1/3Subtle negativity
Expresses mild disapproval or a negative attitude without being harsh. 
John's decision to drop out of college was frowned upon by his relatives.
Pro Tip 2/3Cultural Sensitivity
What is frowned upon can vary widely between different cultures and societies. 
Wearing shoes inside the house is frowned upon in many Asian cultures.
Pro Tip 3/3Not Overtly Offensive
The phrase is polite and indicates disapproval without causing offence. 
Interrupting someone while they are speaking is generally frowned upon.