There are this things called morals. Even though working in the limits of those doesn't come naturally to us, we impose those restrictions on our actions after the entire thought process. With me most of the times I can't really remember what are the rule when you do certain types of actions.
So.. what is the practical way?? Avoid situations where your action and thought might not coincide!!
For the question I've asked above, I totally believe that you are a real stupid to ask such a question if the situation really arises.
To avoid that situation (of even thinking).. I would've never done anything for others.. ;)
ps: If what I said above is true then.. the previous post should be a retrospection of my decisions rather than total sick feeling.. but is it..??