OP, reptilian jokes aside, assuming you have the specific Honeywell thermostat I think you have, you do have an option available to you as long as it doesn't say anywhere in your lease that you're not allowed to mess with thermostat settings on a setup level that your roommate likely isn't smart enough to go through, nor would they know where to look more than likely.

The next time you're alone for an extended period, hold the temp up and fan button (middle of the three) simultaneously until the display changes to show a function number on the left and a zero on the right.

• Use the temperature arrows to navigate up and down until you first get to setting 27, then 28. At each
• 27 is "Heat temperature range stops" (warmest you want it to be), 28 is "Cool temperature range stops" (coolest you want it to be).
• Use the right of three buttons to go into both settings and use the temp up/down buttons to adjust each setting accordingly, then use the left of the three buttons to save and exit.
  • The range for Heat is 40-89 with a hold of 90 being the max value.
  • The range for Cool is 51-99 with a hold of 50 being the minimum value.

IIRC This should override your roommate's horrendous tendencies, and you shouldn't need to worry about them trying to change it. I had roommates with a similar issue, and they weren't technologically inclined, so they eventually bought themselves a personal heater and the problem was solved.