It does seem really petty to report someone for being late to work. I would never do it. I can't recall any time I've ever reported anyone for anything at work. I mind my own business too. If you are not as supervisor, why would you report someone?
While agree, I think details are pretty important here.
Was he three or five minute late, was it a few seconds late? Was he just sliding into work, just over the wire? Was this just a matter of not giving himself enough time to scrape frost off the windows, or being stuck in traffic, the line too long at the gas station, etc., or, is it something completely different?
Or was this a blatant disregard for the schedule, are we talking, hours late?
I have a hard time understanding the magnitude of the problem as it was written.
If folks in this thread bring up some important issues of co-workers picking up slack of chronically late co-workers if they are never there. . . . I don't know.