Just change where you shop!
I've gotten used to shopping here in Germany. If I want to try on a top, I take the L into the dressing room, and maybe even the XL if the L is looking a little small. I can sometimes squish into an M - if I wanted to go for the ultra-tight check-out-my-boobs look. Which I don't.
However, when I was back in the US, I was browsing the Target clearance racks and discovered that the L is much more L. I bought a shirt that was an M and although it is a slightly fitted cut it's all billowy like I have no waist! The medium!! The difference was really shocking.
However, I guess it shouldn't be, according to this nifty chart showing the extent of vanity sizing in the US. At Old Navy, if pants say they have a 36-inch waist, they actually have a 41-inch waist!! This isn't even exploitation of the vagueness of S, M, L, XL sizing, it's a straight-up lie.
Even Germany has vanity sizing, though, apparently. A friend who went clothes shopping in Sweden thought the sizes there - at the same chains - were smaller than here. This is just anecdotal, but it is true that the Swedes themselves are thin. I don't know how they stay that way all winter when the temptation is to go nowhere and eat lots of hot fatty foods... or is that just me? ;)