My Dsis is lovely - sweet and caring and funny, and very, very clever. She has a 2:1 from a RG university, brilliant A levels - she's talented at dancing, brilliant artist, yet has it in her head, and therefore other people's, that she is not very intelligent at all!
As such, anything she could do but doesn't want to do - like changing tyres, checking fuses and so on - is blamed on not being bright enough.
Most frustratingly, men fall for it every time!