Jerk's Constitution

i would change double to expertise

You're*

it's*

wut!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

we get what you mean but saying "you have proficiency in constitution saving throws, If you allready have proficiency, your proficiency bonus is dubbled for any saving throw you make using constitution."

where i a rules lawyer, i'd mention that the term and feature expertise is reserved for abillity checks, and does not apply to saving throws or attack rolls. Shure nobody but WoTC and maybe like twelve other people even care but you are technically wrong.

um wat

Quote from WillowTehKitsune >>

um wat

 Agreed.

You can't be proficient in an entire ability score.

Expertise is a class feature. It is not the official term for double proficiency.

This feat already exists... it's called Resilient. Unless you don't mean Constitution saving throws, you just mean Constitution checks (which is really just concentration checks, as nothing else in the game uses constitution skill checks). So either way, the OP is wrong.