A kick in the Kellogg's
When somebody is brutally honest or mean regarding something you are sensitive about, and you get your feelings hurt:
e.g.1: They made fun of my accent. I pretended to be part of the fun but it was a kick in the Kellogg's.
e.g.2: Boy-oh-boy, the teacher really kicked me right in the Kellogg's when she said that I can't sing.
e.g.2: Boy-oh-boy, the teacher really kicked me right in the Kellogg's when she said that I can't sing.