once i and my two roommates were invited by a female co-worker. We were wondering what was going on as it was unusual to invite all of us. When we get there, we saw other co-workers, about 3 females and 3 of us. Then comes the stranger, he worked in another department of our company and he only knew the female who invited us. Then everything is clear, he is here to pay the bill. And the story between him and my female co-worker ended there.