As much as I am a writer, and cringe at common grammar mistakes and spelling errors, I can (after mentally correcting them with a flourish and an imaginary red pen) shrug most of them off with a simple there, their, they’re.
However, there is one really common grammatical mistake that is, to my mind, as gratingly painful to my senses as fingernails down a blackboard (yes, I’m showing my age, and yes, that saying will probably die out with my generation, as most kids these days have never experienced the torture produced when nails meet a blackboard!)
But back to the subject at hand. I can barely tolerate it when I hear ‘should of’, ‘would of’, ‘could of’, but I can at least attribute the error to mishearing the contraction (should’ve) or even a simple mispronunciation of the word ‘have’.
When I see it written down, however, there’s no making excuses for it. It’s just downright bad English.