Cockney is both used as an accent and an area description. A mug is like 'your a mug', like your stupid, foolish.
No, 'proper naughty' isn't an official meaning of mean people in the UK, it's just a phrase a small amount of people use, and normally satirically.
Current favorite wrestlers: Brock Lesnar, CM Punk, Daniel Bryan, Dolph Ziggler, Alberto Del Rio, Roman Reigns
All-time favorite wrestlers: Stone Cold, The Rock, Kurt Angle, Triple H, HBK, The Undertaker, Y2J, Eddie Guerrero