My pet hate is people who say 'pacific', when they mean 'specific'. GRRRRR! Also, people who say 'skelington', instead of 'skeleton' and (this one seems to be getting more and more common) people who say 'pleece', when they are referring to the 'police'. Don't get me started on grocer's apostrophes (tomatoe's) as I can rant for England about those!
Please don't think that English is in any better state here than it is across the Atlantic. Even our newspapers contain very basic grammatical errors and seem to become more and more colloquial all the time; one particular newspaper refers to women 'falling' pregnant or couples 'splitting up from' each other. This makes me really crazy; given that the vast majority of people do no further reading than the newspaper, it is a very poor example. I think a lot of the deterioration is also due to the popularity of text-messaging in this country.
cheers
Rosie