...when web sites put on the bottom of the page:

(a) "You need Internet Explorer 6 or Netscape 7 to view this page". (Er, no I don't; your website is fully, 100%, totally, utterly, completely, nothing-missingly functional in Firefox/Mozilla/Epiphany/Galeon/Safari/Opera)

(b) There's a W3C HTML 4.01 compliant button on it :-)

[That's a true story from a website I use for work. You folks unfortunately won't be able to use it; it's a passworded thinger]

I'd much rather people put "tested in foo, bar and baz browsers, but should work in any recent browser".

NAI even go to the extreme of putting up a big old "UNSUPPORTED BROWSER" popup that uses CSS2! Go figure.