Regular expressions are by far my favorite tool.
Very tricky to get used to, but once you're there pretty much any other string parsing thingie seems completely useless. The only problem is when expressions get very long.
@Dygear, sections on regular expressions in the PHP manual is basically for people who already know how to use them, it's more just a list of modifiers and basic syntax, google for some tutorials or buy a book instead, it'll be worth it.
Most hated function call? fork(), it doesn't work on Windows. (PHP)
<?php
php
$str = stream_get_contents(fopen("http://liveforspeed.net","r"));
echo preg_replace(array(
"/\n/ms",
"/<.[^>]*>/ms",
"/.*April.[^W]*|(?=\!).*/ms",
"/a(r)e/",
"/th(?=[ai])/"
),
array(
" ",
"",
"",
"\\1",
"d"
),
$str) . "!!1! (rly?)\n";
?>