A phrase of warning used to prevent oneself or others from asking or doing something that might provoke a negative response from someone or something else.
Employee 1: "Should I ask the boss for a day off?"
Employee 2: "He just found out his wife left him, so don't poke the bear."
A phrase uttered to ward off people who are needlessly angering, upseting, or annoying you... sometimes even going out of the way to do so. A different way to warn people that they're on thin ice, or that a joke is going too far.
John, eating pancakes: Ughh, these are terrible...
Macy: I'm sorry I tried not to burn them this time...
John, laughing: The syrup isn't even seeping in!
Macy: Hey, you never cook so don't complain!
John, still giggling, takes another bite and makes a gagging sound
Macy: Hey, don't poke the bear!