it's just automatically playing in my head whenever I encounter any kind of condition irl, in manga, or anime that matches the slightest with the song.
Yui version of My Soul, Your Beats when she auditioned.
Been stuck in my head for days.
Gunglinger Girl Teatrino ending. I always loved how they ended it perfectly, though they got lazy near the last few episodes.
AND
Spoiler:
Amazing, I can fit more than three songs in my head. Just for higgles and giggles, the OP to Gunslinger Girl gets stuck in my head sometimes. A lot of FMA BH themes do too.