Today's Tank McNamara features an idiom with two very different meanings:
There are a number of words like sanction and table that are in some sense auto-opposites. And it's common to invert the emotional valence of terms like sick or queer. But this is the first time that I've had an unironically self-inverting phrase brought to my attention, as far as I can recall.
Yesterday's Doonesbury explored an expression that has only one conventional meaning, but might naively be interpreted in a very different way: