Women know this better than men, but the tape measure knows all: clothing makers can be outright liars when it comes to sizing. Esquire magazine's Style Blog took measurements of seven mainstream 36-inch pants and found discrepancies of up to five inches.
The king of loosey-goosey sizing was Old Navy, which was off by the full five inches on their "dress pants". Other brands varied in their adherence to reality-based measurements, but the lesson is the same across all brands. Clothing manufacturers want you to feel good about your sizing, regardless of the reality of your waistline health or the other clothes you own that might now seem so weirdly incongruous in how they all fit.
I remember a tailor, one week prior to a wedding, explaining to me that my "jeans size was on a different planet than your dress size", and that line makes a good bit more sense now. What's the worst sizing you've seen in a store or with a particular brand?