Oh I so desperately need a PHP equivalent right now.
PHP actually allows much less mischief here than C or, say, Python does. It doesn't let you redefine or delete functions, classes or constants, unlike C where macros can be abused for this, and Python where you can delete anything. But you could hide all errors if you want to screw with people: error_reporting(0); set_ini('display_errors', '0'); set_error_handler(function () { return TRUE; }, E_ALL | E_STRICT); set_e…
var_dump(true == 'false');
Or you can overload library functions by abusing namespacing or runkit, but yeuch.