I'm not one who holds fast to the rule about not wearing loafers with suits, although the loafers in question don't strike me as being a particularly good pairing with most suits.
Penny loafers and jeans is a very traditional combination. Not everybody cares for it, and presumably the person who told you your loafers were too formal to wear with jeans doesn't care for it. But it's been a widely accepted pairing for 60+ years now.
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Michael












