When you leave early from the bar with some skank, fuck her bareback, don't clean yourself off, then go home to your girl and fuck her bareback leaving your dick crusty like a fried banana!
I totally fucked Rebecca until about 11 then went to Karens and gave her the "fried banana" in her mouth!
An update on the expression as happy as a dog with 2 dicks, popularised from the youtube video of a monkey that upon receipt of a 3rd banana runs round its cage then masturbates furiously