An open letter to students
Some space on campus, like your dorm, can be safely assumed to be student-only. Other space, like the library, cannot. The old guy next to you in line at the library cafe just might be, say, a professor. Might even be the professor of the friend whose fraudulent excuse for skipping a scheduled exam you were describing in detail (though in this case wasn't that particular professor); in any case, might be a professor, who won't be entertained by such stories, or by the tales of your own past similar fraudulent feats of derring-do.
Now you know. And knowing is half the battle. (That's an in-joke aimed at other old people; don't worry about it.)