just quietly
A combination of words often said just before or after a confronting sentence so as to (apparently) soften the blow whilst also snidely stressing your point.
Ben: "Hey man. I know I've been drinking. But should I go there."
Tom: "Dude. Just quietly? She has a forehead the size of a bus."
Stranger: "Those glasses make you look like a rapist. Just quietly."
Tom: "Dude. Just quietly? She has a forehead the size of a bus."
Stranger: "Those glasses make you look like a rapist. Just quietly."