it basically means that they are as boring as a dead person, as 'stiff' is slang for a dead body.
Dull, boring, plain, common.
that you are a boring person
boring
This is old slang for a girl who is boring, unlikely to put out or unattractive. It's similar to calling someone a wallflower, party-pooper, wet blanket, killjoy, etc.
When someone sucks the fun out of the party/place your at. And its no fun around them. They are boring.
No it can't call someone
No it can't call someone
stiff
Calling someone a "pig" is often used as an insult to suggest that they are messy, unclean, or gluttonous. It can also imply that they are greedy or uncouth in their behavior.
meaning stiff
According to the urban dictionary it does mean boring.
To get a Stiff, or Stiffy, is school playground giggles for an erection