When in the middle of having what you think is an heartfelt, loving conversation, he suddenly stumps and stuns you with an off handed remark that has a serious doubling meaning (and you get the feeling he wanted you to get it) and the conversation suddenly takes a turn for the worse. He then begins to tell you how he didn't really mean it the way it came across, but you're so stunned all you can focus on is WHAT he said! He always means well so you're easily convinced this was a slip of the tongue. A fart of the mouth if you will. A "humstun" truly is a slip of the tongue, or accident unlike the humslip
where the double meaning slips right by you but was said purposefully.