Please don't ever make this assumption. I referred an acquaintance from school to my workplace (he was a great project partner, and I was the first of us to get hired after graduation, so why not?), and apparently when he passed through everyone was just... doing work. That was a telltale sign that everyone was grumpy to him.
I had to explain that we basically don't work at all on Friday afternoons because we're too busy drinking, we play pingpong religiously, frequent out of office events on the weekends, and in general it's just an enjoyable crowd. Random conversations happen all the time.
But nope, that one time he came through the office, everyone looked unhappy. Because they were working, I guess.