Probably been many threads on this very subjest but I get irrationally irritated when people use an apostrophe when not required. A roadside sign on my way to work reads 'Puppy's for sale!' Puppy's what??!
Also on big sign in shop window - SALE! Hat's!! Scarve's!!(yup) Book's!! I mean COME ON. Don't any of these people read? Goodness I sound like my Grandmother....