Inflating the foreskin - possible only for an uncircumcised man. (Air should not be forced down the urethra, and on no account should high-pressure air supplies be used.)
"giz a balloon job"
"i corr, my compressor is knackered"
Act of blowing air into a woman's vagina until her belly swells and then yanking on her pussy lips in a futile effort to make the squealing sound made by a balloon under similar conditions. It never works.
Biff: Chaz is an asshole! He told me if I gave my girl a Balloon Job she'd love it. But she just farted at me and left!