I... have no idea what happened.
I was tending my bees, opened an apiary, MC crashed (unexpected error).
Had a friend break the apiary I thought was causing the issue, crashed again (same thing).
Had him break the rest of my apiaries... crashed again.
I think I've narrowed it down to Optifine and Soartex texture pack conflicting pretty hard.
If I have only Optifine installed, it works fine. if I have only Soartex installed, it's fine. Put them together, MC implodes.
I don't understand why, though. They worked fine together up until a little earlier today.
Original crashlog below the spoiler tag.
Also updated tags/title to reflect my findings.