I've noticed a curious, not to say disturbing, trend in the recent online behavior of several correspondents. When discussing activities conducted on a regular, weekly basis, many people now include apostrophes where, as far as I can tell, none are required. For example, someone writes, "On Monday's I take my sloths to the sloth-washing facility for their weekly sloth-wash." There's no reason for that apostrophe 's': The writer is not saying "On Monday is I take. . .," nor is she describing something in the possession of Monday. The right word is "Mondays."
(I note, by the way, that when I typed "Mondays" above, I was not even chastised by Microsoft's famous red squiggle, further proof that the pluralization is perfectly acceptable. Although, "pluralization" is apparently not, but that's another story.)
I hasten to point out that the people engaging in this random apostrophizing are generally well-educated and, indeed, skillful writers. Whence, therefore, this unnecessary punctuation? Answers are welcome. Write me any time. I can be reached on Mondays, Tuesdays, Wednesdays. . . .