it basically means that they are as boring as a dead person, as 'stiff' is slang for a dead body.
strong or potent to the taste or system, as a beverage ormedicine: He was cold and wanted a good stiff drink.
Dull, boring, plain, common.
that you are a boring person
boring
Calling someone "vanilla" can imply that they are plain, boring, unadventurous, or lack creativity or uniqueness. It often suggests a lack of excitement or originality in their behavior or personality.
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
meaning stiff
According to the urban dictionary it does mean boring.
To get a Stiff, or Stiffy, is school playground giggles for an erection