Yeah, I was the same until a machine failed and a colleague said that the coin might be fake.
There is something rather delicious in the fact that we're so used to machines and computers failing that the idea the coin could be wrong never entered our heads!
So I put my money in the drink machine and hit the coin return. Nothing happened. I tried a few times and figured the coin return was broken or that it was out of coins. The only thing in the machine was soda, which I can't drink if I don't want to trigger my acid reflux. But I bought one anyway since otherwise my money was "wasted", thinking I'd give the soda to a friend later.
Of course, once I bought the soda, the machine spat out all my change: 3 quarters and 2 dollar coins - now I finally had coins that I could buy food with. Naturally, the food machine didn't accept dollar coins. Most machines here don't, so no food for me.
Prior to about 2010, 5p and 10p coins really were thinner. They were changed from copper/nickel alloy (Cupronickel) to nickel-plated steel to reduce costs. But in order to maintain the same weight, the coins had to be made thicker.
You can get answers on so many topics on HN...
I have indeed had some pound coins which were tatty round the edges and had to be pushed through a self-service checkout several times or wouldn't even go through at all. I still hadn't realised they might be fake, though.
I have noticed that a lot of old 10p coins are noticeably a lot thinner (presumably worn down rather than starting out thinner) than new ones. Is this as it should be or should I start looking at these with suspicion too?