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 balloonjob"
"i corr, my compressor is knackered"
The result of a girl attempting to give a guy a hand job, but for reasons unknown, possibly because they're mentally retarded, makes it hurt more than almost anything known to the male race. the name is self explanatory in that it feels like sand paper is actually being rubbed along your junk. may result in bleeding.
If you feel as though you are headed towards a sandjob, GET THE FUCK OUT.