Katy Perry may have the party anthem of the Summer in "Last Friday Night (T.G.I.F.)," her latest single from Teenage Dream. If the catchy tune doesn't make you happy, then the video will. In the '80s movie homage, she gets into character as Kathy Beth Terry, a glasses-and-braces-clad nerd who wakes up with the fuzzy memories of an epic party the night before. The real highlights of the clip are the star cameos, which include Glee stars Darren Criss and Kevin McHale and viral video sensation Rebecca Black. Those are only a few of the celebrity sightings though, so watch the video to catch the rest!