French hello
It's just a blow job.
Guy #1: I didn't even get to take her on a date before she gave me a French hello.
Guy #2: OHHHH! NICE.
Guy #2: OHHHH! NICE.
French Hello
To enter a room full of people you know without saying hello or making any gesture of acknowledgement
You walk into a pub full of your friends. As people turn around and start saying hi or reaches out for a handshake or a kiss on the cheek, you ignore them walking straight to the bar and order a beer. That's a French hello!