Drums.
Started playing snare and general percussion when I was 8 years old. School band / orchestra, so classical training. Kept doing that all through high school. Got a drum kit at age 12, along with 1 on 1 lessons for about 4 years. I would practice on my own nearly every day up to about 17, 18 years old. By then I was playing in bands and was getting most of my practice in a jam room setting and was playing shows.
26 years old now and for the last 3 or 4 years I've never really 'practised' at all. Recorded 2 albums in that time, recording the songs as I learnt / wrote them lol. We'd play live every 4 months or so and often I wouldn't even pick up the sticks until the first time we have an all band practice, usually about 2 weeks out from the shows.
It's a strange feeling, because I know guys that put in mountains of practice that aren't on the same level as me, which sometimes makes me feel a bit dirty in some ways. And I also know that I could be much better than I am if I was to put more effort into it, but I don't.
It's something that is seared into my brain at this point. I hear timing and beats in everything. If I walk into a room and there's music playing, I'll be walking to the beat of the song without even realizing it. Even my hands are effected, I have a pretty low range of movement on my outer three fingers on each hand, because they've spent so long holding drumsticks that they don't know anything else.