I've had an old habit of veering towards "stomach flu", as you're not expected to have symptoms after you get better. Also IF your boss randomly asks for a doctor's note, the doctor isn't going to stick a finger in your butt to make sure that you, in fact, have diarrhea. And the doctor is likely just going to give you the note.
My problem is that :im-vegan:, so when I'm constantly calling in for stomach bugs, my workmates are always saying "I thought you guys don't get stomach parasites". Also I'm literally the most covid paranoid person I know IRL, N95 mask everywhere and eating in my classroom alone, with windows open if possible. So it's a lot less likely that I'm going to get a cold or the flu.
So what am I going to do next time I need a lie-in? Say I broke a rib? UTI? Aggressive acne?
It's not generally illegal to lie, but it is generally illegal to lie of it benefits you and someone else loses out because of it.
Lying under oath is a bit different since the prosecution doesn't nerd to prove that you lied maliciously or for your own advantage, only that you lied.