Ah man is derived from the words ah and man slung together in a wonderful, delightful phrase.
Mostly used by stoners, the said
prase is an assertion of said
stoner's stonerness, while also being an affirmation of something (similar to yes, but cooler).
For best effect, say in a
zonked out, rusty tone of voice - ahhhhhhh man!
Stoner 1: Thy alright?
Stoner 2: Ah man.
Stoner 1: What thy up
t'?
Stoner 2: Chillin' art
wi' a bag o braan
Stoner 1: Ahhhhhhh man buzszin'
tits off B-)