Weak in the knees 

Being weak in the knees means whenever you see something attractive or after you have sex and/or cum your legs feel weak

Hey do you see that hot girl over there?!

Yeah look at her fat ass

Man she’s got me weak in the knees

Weak in the knees by Billybobjr69 November 6, 2018

weak in the knees 

What one says/feels after they had amazing sex and/or a splendid fap session, the feeling is so intense you can barely stand up, thus weak in the knees.

Guy "Dude, you all right? your legs are wobbling"

Dude "Yeah I'm all right, I just received the best blow job from my gf; made me weak in knees "

"Damn, I jizzed so hard last night my legs couldn't support me for the next 3 minutes."

"Damn, I banged my gf so hard last night I thought my knee caps would explode"

weak in the knees

weak in the knees by SirCumsALot April 13, 2013