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Skag sack: 1 (skæɡ)

Noun, slang

A skag sack is a term to describe a person in a negative manner.

The term is used to insult someone for doing something incredibly stupid. Majority of the time the person will not understand what you're saying but the term skag is generally a negative term. A good way to put someone down and leave them confused.
"You're a skag sack"
by Ohhej February 25, 2013