Question: I have met the following HTML code:

```
<a rel="douche" href="...">blah</a>

```

And I am wondering what is the effect of the "douche" attribute.

Answer: 
It's just "commentary."  

In this case, whoever created that link apparently thinks the person on the other end is a douche. The `rel` attribute defines the relationship between the current document and the target(`href`) document. 

Consider this a more…aggressive version of the [Vote Links microformat](http://microformats.org/wiki/VoteLinks). (Just as non-standard, but was an attempt at establishing a recognizable convention for links to express dis/agreement.) You can stick pretty much whatever you want into the `rel` attribute; there aren't that many standardized values for it. In general browsers don't do anything with `rel` data; search engines might, but that would still depend upon values they're expecting. This one is unlikely to say the least.
It has no meaning assigned to it in any published specification. It may have been agreed on in some community, or it may have special meaning to some software, or it may be just someone’s idea of a joke. There are various `rel` values around, but anything that is not listed in the Microformats Microformats Wiki [existing rel values](http://microformats.org/wiki/existing-rel-values) page probably isn’t worth thinking of (and this one isn’t).

It has no effect as such, but it is available to any program that cares to read the HTML source, and programs could then do, well, anything with it. Most `rel` values are write-only, with no effect unless you create one, with styling, scripting, or other tools.