You cannot, because it's a matter of perspective and you can't possibly place yourself in positions of all perspectives. Can I go for a 5-mile walk right now?
Sure. If in doubt, say "John invited me"... everybody knows a John. Edit: Are you making the sandwich out of yourself? Out of us? Out of bread, but we're both present? There's too many variables. Can I drink 3+ cocktails tomorrow evening without feeling tipsy? I've not had any alcohol in a while.
