Means: Someone who is very cool - or very uncool
Usage: "You took the blame for me - you're a ledge!"
It seems very typically British, somehow, for one of the very few Yoofspeak terms that expresses open admiration to double up as a sarky putdown. The shortened form of "legend" or "legendary" started out as a straightforward endorsement for someone who shows outstanding skill (as in skater slang where it may have originated) or just an unexpected kindness, replacing "You're a herostar!" (or "star-spa" as north London kids used to say). When it's meant sincerely like this it is sometimes accompanied by a brandished L-shape made with finger and thumb. Peer envy is even stronger than peer admiration, though: no one likes an over-achiever or a show-off, so these days "ledge" (sometimes "ledgemeister" or "ledgebag") is just as likely to take the form of a sneer. Our kids may have picked this up from older siblings familiar with those ironic phrases popular more than a decade ago: "a legend in his own lifetimelunchtimein her own mind".