I actually have a fun hobby of dreaming about unethical-but-legal startup ideas. Then again, whether something is unethical depends on how you define your own ethics, or alternatively, invent some self-justifications.
Munchkin ideas are often unethical but legal. This is because a Munchkin is by definition a way of following the letter of the rules while violating unspoken convention. In some cases, ethics, in contrast to law, means precisely that one follows uncodified rules of behavior.
Thus spake Eliezer:
It seems that many here might have outlandish ideas for ways of improving our lives. For instance, a recent post advocated installing really bright lights as a way to boost alertness and productivity. We should not adopt such hacks into our dogma until we're pretty sure they work; however, one way of knowing whether a crazy idea works is to try implementing it, and you may have more ideas than you're planning to implement.
So: please post all such lifehack ideas! Even if you haven't tried them, even if they seem unlikely to work. Post them separately, unless some other way would be more appropriate. If you've tried some idea and it hasn't worked, it would be useful to post that too.