Stuff that you'd try and do KNOWING that you couldn't...
1. Knife Sherry in the face
2. Shoot Ada (in the face)
3. Go back through a door you KNEW was now inaccessible
4. Combine random, stupid items (e.g. the handgun and a Green Herb or something)
All further additions welcome...
If ignorance is bliss it's astonishing that there aren't more happy people in the world...