Ginger Snap???

So I was out to eat with one of my teacher friends and my mother-in-law last night. My mother-in-law started talking about how she wants our baby to have red hair like my nieces who are 4 & 2 and both redheads. It's genetically improbable for my husband and I to have a red head. 
My teacher friend told us that teachers have a common phrase "ginger snaps" for redheads, because "in general red headed children are more prone to acting out".
Now I've read the "Gingers have no soul" comments on the internet, but I never heard a bias like this in real life.
Is this a wide spread ideology among teachers?

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