When I started to learn programming (by myself), I had a really hard time understanding what foo and bar were and what they meant in various tutorials and blogs. I was already trying to learn the syntax and programming concepts, throwing some unknowns words in the mix did NOT help. For some time I thought foo had special meaning in PHP, or that it meant something in English (not my first language, and I was much less proficient in English at ~14 than I am today).

Using foo bar baz qux is lazy when you can easily find countless examples.