An idiom or a figure of speech that conceals where you are truly going and what you are really going to do. In all honesty, you are sending the message that you are heading for the toilet to lay waste in. This phrase is derived from a much similar phrase, does a bear crap in the woods?, which is a question that is posed after someone states the obvious.
See Going to see a man about a dog and Going to see a man about a horse for similar phrases.
"I'll be right back. I'm going to see a man about a bear in the woods."