Usually when you tell someone that something in a video game grossed you out, it’s something gory or nasty. Mixtape ‘s big gross-out moment, however, doesn’t come from violence or illness, though it might give you a violent illness if you’re sensitive to slimy sounds and the awkwardness of inexperienced makeouts.  Early on in Beethoven & Dinosaur’s new music-driven narrative adventure, music curator and soon-to-be New Yorker Stacey Rockford is reminiscing with her friends about high school. Stacey likes to tie moments to songs, and when she finds a mixtape given to her by an old “flame” named Colin, she remembers how he was her first kiss.…