Stuffing some dripping meat drapes with your blue veined custard chucker.
"I jus took you to a fuckin $30 a plate dinner - are we gonna slam or what?"
"I was slamming the hell out of this skeezie..."
This pratice is not endorsed by the Royal Mail but is common place amongst posties, especially on a Saturday in an effort to secure an early finish.
Slamming involves reintroducing the letter into the mail system the next day back at work.
The undelivered item is refered to as a slammer.