Brighton slang for cheeky, particularily in the case of younger people 'giving lair' to older people. Lairing someone up is like winding them up, maliciously.
Southern English slang used to mean "Don't fuck with me" and aimed at someone who is being insulting or confrontational. Often the person who uses this word thinks he is a bad man and the person who it is aimed at has damaged their fragile ego somehow.
Chav#1: Damn man, your girlfriend has had more cocks in her than the barn her family lives in!
Chav#2: *grabs chav #1 by the collar* Listen bruv don't get lairy or i will fuck you upright here and now!!!