To think 3 months salary for an engagement ring is a bit bonkers?

[VenetiaFleet]

Was chatting to a friend earlier and she mentioned that the "rule" for buying engagement rings is that the man (she was talking hetero weddings) should spend three months salary on a ring. Apparently this is the done thing but I alone in thinking this is ridiculous? If DP were to ever propose then there's a lot of other things I'd rather he spent three months salary on than a piece of jewellery!

I don't really like wearing jewellery and I'm not hugely fond of diamonds either (much prefer a ruby or garnet) but I'm an unromantic soul who works out purchases at price per wear so to me a few grand on a ring doesn't shock me too much as it's an item that's going to get daily wear.

I'd always buy antique though, you get so much more for your money.