This is an example of doing silly things with headers in WordPress

WP-fun-with-headers.php

<?php

/** 
 * This is an example of doing silly things with headers in WordPress
 * 
 * @author Lord Matt <http://lordmatt.co.uk>
 */


function fun_with_headers(){
    
    $jokes = array();
    $jokes[]='Did you hear about the restaurant on the moon? Great food, no atmosphere.';
    $jokes[]='What do you call a fake noodle? An Impasta.';
    $jokes[]='How many apples grow on a tree? All of them.';
    $jokes[]="I just watched a program about beavers. It was the best dam program I have ever seen.";
    $jokes[]='Why did the coffee file a police report? It got mugged.';
    $jokes[]="How does a penguin build its house? Igloos it together.";
    $jokes[]='Dad, did you get a haircut? No I got them all cut.';
    $jokes[]='What do you call a Mexican who has lost his car? Carlos.';
    $jokes[]="Dad, can you put my shoes on? No, I do not think they will fit me.";
    $jokes[]='Why did the scarecrow win an award? Because he was outstanding in his field.';
    $jokes[]="Why do skeletons never go trick or treating? Because they have no body to go with.";
    $jokes[]="What do you call cheese that is not yours? Nacho Cheese.";
    $jokes[]="Why could the bicycle not stand up by itself? It was two tired.";
    $jokes[]='What did the grape do when he got stepped on? He let out a little wine.';
    
    $thisjoke = $joke[rand(0,count($jokes)-1)];
    
    header( 'X-Silly: These headers are very silly' );
    header( 'X-Also-Powered-By: Mutant Gremlins' );
    header( "X-dad-joke: {$thisjoke}" );
}

add_action( 'send_headers', 'fun_with_headers' );