Does it really matter. Or is it that only your opinion matter. But here's the definition of pettier. And here's how you would spell you. "You"
pet·ty
/ˈpedē/
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adjective
comparative adjective: pettier
1.
of little importance; trivial.
"the petty divisions of party politics"
synonyms: trivial, trifling, minor, small, slight, unimportant, insignificant, inessential, inconsequential, inconsiderable, negligible, paltry, footling, fiddling, niggling, pettifogging, nugatory, of little account; More
2.
of secondary or lesser importance, rank, or scale; minor.
"a petty official"
So basically look and read the above. Before you try to correct anyone's grammar. I suggest you start with yourself first. Blessings to my grandmother for being a teacher.