Don't "drunk dial" an old lover.
Double check the "To" address before sending an email about your incompetent boss.
And if someone really ticks you off, sleep on it before posting about what happened. You might decide in the morning that it's best left unsaid.
That last bit of advice comes to mind with the story of a Seattle bartender who exposed a "nasty non-tipper" on her Facebook page and mistakenly identified the wrong guy — causing headaches not only for him but for her as well.