Grimaced & Grimmest

Grimaced – (v.) past tense of Grimace, an expression of displeasure.
Grimmest – (adj.) the most grim.
So, yes, maybe I grimaced because I was the grimmest.

Breach & Breech

With an A – (v.) break through from one area into another.
With an E – (n.) hind section of an object or animal.

Berth & Birth

With an E – a sort of smallish sleeping space, or other designated area such as for docking boats.
With an I – a sort of smallish person undocking from its mother.

Scoot & Scute

-oot – (v.) a little bit sliding, a little bit shuffling, just kinda nudgin' along, y'know?
-ute – (n.) a bony plate such as the ones that cover a turtle's or armadillo's shell.
Speaking of which, whaddaya think of that cute little turtle? 'Scute, isn't it? :)