at the end of kidney it is definitely a vowel - it makes an "ee" sound. Where "y" is a consonant is usually at the beginning of a word (like yellow) where you have to move your tongue to make the sound.
According to Meriam Webster: "When y forms a diphthong—two vowel sounds joined in one syllable to form one speech sound, such as the "oy" in toy, "ay" in day, and "ey" in monkey—it is also regarded as a vowel. Typically, y represents a consonant when it starts off a word or syllable, as in yard, lawyer, or beyond." https://www.merriam-webster.com/words-at-play/why-y-is-sometimes-a-vowel-usage#:~:text=When%20y%20forms%20a%20diphthong,yard%2C%20lawyer%2C%20or%20beyond.
I just always treat Y as a vowel if it is creating a dipthong, and if not (which is quite rare) then it is a consonant. If we want to get technical though, it's something called a glide (or a semi-vowel).
I know this is kind of an odd request, but all I could think of was “goatee” for “GT”. Maybe that could be added? I’m not sure if you’d consider it a body part though.