My sister is a lovely, seemingly intelligent woman who has reached critical mass as well. She has a few that she constantly confuses us with:

Condoms--Condiments--Condominiums
The 'Condiments Upon Request' sign at a drive-thru window sent her on a rampage about passing out free contraception to just anyone...

Veterans--Veterinarians--Vegetarians
She once called to inform me about special benefits..'Didja know they have Veteran's life insurance now?' And of course, veterinarians are the ones that don't eat meat.

~Elle (she who never remembers the people, but can name every dog they've ever had)