"Don't poke the bear" Meaning:
Don't annoy someone who's already irritated, try not to aggravate someone who's easily angered. Examples:
"He just found out his wife left him, so don't poke the bear."
"If you don't want to hear your father shout, don't poke the bear. "http://www.english-for-students.com/Poke-The-Bear.html