He was sat beside the fire. (I can always find another one...)

Some of them are probably dialect terms that possibly evolved from old/middle English in a different direction from the one we're used to. In Scots, th, y and z could be used interchangeably - there's a stone I saw in an old graveyard years ago marked to 'Ye zounger dochter of... ' It was dated somewhere in the 1400s. In dialect 'ye' or even just 'ee' is still used quite often for 'the'. I suspect 'I could care less' came from a TV comedian.

But what gets me more than bad grammar is misused homophones...