What do you think of people who pronounce 'yes' as 'yah'?

I was in a coffee shop, and the woman ordering coffee in the queue in front of me was being asked if she wanted milk, her response was, "yah!". Would she like a cake too? "Oh, yah!" Does this LAME pseudo-posh mangling of the English language bother anyone else, or am I the only one who wanted to sit her down for a nice chat on how it is wrong, wrong, WRONG?