

If you’re following them around, that’s not living rent free in someone’s head, that’s just being weird.
The whole idea of the phrase is the one living rent free is just enjoying their life while the OTHER person obsesses about them.
If you’re the one doing the stalking, it’s the stalkee that’s living rent free in your head.
Stylistically, I’d give the 2010s to hipsters. Damn I do not miss skinny jeans.
Item and sociologically? The smartphone is now ubiquitous.
Sadly, I think the late 10s + a bit will be known as the trump/covid era. (Or, if things get much worse, the beginning of the end.)