Person from the Black country which is in the west midlands, very close to birmingham. The Black country dialect is very unique. Yam yam derives from 'you am' e.g 'yam coming with me ay ya?'
A couple of drug smoking munch seeking yam yam's in a car:
"Yam gewin the wrung way! Where am yo gewin kid?"
"I ay at all!"
"Ye yam, yo day tek that last turnin ya saft get!"
"Oh arr, soz I day realise"
"yo'll atta gew back im starvin I cor wait no longer kid!"
A person from the Black Country area of the West Midlands of England. Yam-yams use a slight variation of English that is often incompehensible to non-locals (and even to their neighours from Birmingham, with whom they share many similariies in vocal accent) due to both the thick accent of the speaker and the frequent exchange of standard words in place of local terminology (the most obvious example being the substitition of the word "you" for "yam").
"I wish these yam-yams would bloody learn some English."