"Ťupka"

This sound caused wars on Reddit and made us the persona non grata of linguistic and conlang subreddits because we (are plural, and) have a sound that is extremely easy and natural for us to say and simply isn't in the IPA and is impossible to transcribe.

The creator of Gëŕrek didn't know IPA, he just used the sounds that are most common where he lived.

Today's contestant is: t̪ˢʼ

Note that the sound isn't affricated enough to be a t͡s and speakers approximate t͡s as ᚦᛋ (t̪ˢs). Also note that the sound is pronounced with your upper and lower teeth touching each other, and the tip of the tongue touching the border between them, but not with the tongue in between the upper and lower teeth as in θ, the teeth are touching, and the tongue is not visible.

Also note that it is contrasted with ᛏ (t͇ʼ) (alveolar) even for speakers who pronounce ᛏ as dental (t̪ʼ).

"Dát ťafku"

"Lukáš zase ťápe máču"