I believe it was my point that a political philosophy cannot adequately be stated in "50 words or less". You have to start from the state of nature, and determine why government is necessesary, and those realms where it should have a say. Once you have carefully proscribed its limits, you have to look at the different ways in which those limits can be maintained over time, and how to balance those few necessary powers against personal liberty, with a heavy hand on the personal liberty side of the discussion, because if you don't government 'needs' (read some busy-body or statists desires), will quickly overpower any liberty an individual might otherwise have.
IMO, you can't go far wrong with using John Locke's Second Treatise on Government as a starting point and build from there.
However, if you'd like something pithy, how about:
- Mind your own damned business
- Keep your hands out of my back pocket.
I like the non-aggression principle as a starting point as well, but don't particulary care for where some libertarians have taken it.