Playing the harmonica.

Your mouth cavity forms part of the instrument (like the body of an acoustic guitar) so you need to precisely control your lips, tongue, jaw, etc on top of the usual embouchure skills that you need for a wind instrument, while also being sure to only use the hole/holes you want. You get different notes when you blow and draw (suck), so you must control your breath so the note doesn't squeak - unless you're doing that on purpose, which lets you play notes outside the key of that particular harmonica. You also need to balance your in and out breaths so you don't get too full or empty of air (a few notes have both in and out options to help with this).

I'm very bad at the harmonica.