Oh! I knew I shouldn't have read this thread when I saw the title. I could be here replying for months.
The one that sticks is my mind was when I was at catering college (ages ago) and one of the students asked the lecturer, "How do you spell 'bowl'?" (Huh?)
She replied, "B-O-W-E-L".
I was shaking my head in disbelief. Didn't know whether to laugh or cry. Of course it didn't go down too well when I corrected her error. It's childish, but in my household we still sometimes refer to bowls as bowels.
A more modern irritation is this new(?) tendency to add superfluous words to verbs. In ye olden days we'd reduce something. Now it always seems to be reduce down. I mean, how can you reduce something up? It's just reduce isn't it?