To say something completely out of context with the conversation after not really taking part in the conversation to that point. For example, two people are talking sports and then someone interjects with something completely irrelevant like "Yeah, I had pancakes for breakfast yesterday." Usually the one being "beckish" is not aware that their comment is out of context and they think they make sense. So, it's an insult to be Beckish. Also can be referred to as "Beck".