Here are some of my favorites:
It's a good thing we have small kids, and as such are not in the habit of having guests in the evening for cocktails. Really, the horror of something so gauche as unmatched glassware is more than any respectable host could bear!
In the old days, when I worked in a junk shop (not a thrift store, a downright junk shop) we were always getting three of things. Some people would only buy two, but I always bought all three. I called it a "drunkard's pair", because you could get drunk and break one and still have a set.
Now if only I could come up with a clever name for the last glass standing.