Having an origin in football sporting rivalry, a word that describes a prominent element of British pub culture. Usually in a group of people over a drink the objective is to slander and belittle one or several of the people to try and impress and entertain others in the same group. The sharpest, wittiest and quickest person that is the most successful in belittling and offending others is considered elevated in the perceived pub social heirarchy.
Commonly referred to as "piss-taking", or "sledging", and one of the English sins featured in a recent British Television documentary series titled "The Seven Sins of England".
The Celtic supporter left the pub because he could not tolerate the slaggish behaviour of the Rangers fans.
The act of having sex with 3 or more men at the same time. Having sex with 2 men, a threesome, is perfectly acceptable, but any more than this is slaggish.
"Of course one of your mates can join in. The other one can get out though, three would be slaggish."