“Saturday Night Live” celebrated its 100th digital short with a star-studded tribute. Justin Bieber joined the party as the fellas took a trip down memory lane. Justin Timberlake reprised his “Dick in a Box” character alongside Andy Samberg while reflecting on some of the more memorable shorts starring Lady Gaga, Natalie Portman, and Michael Bolton. Usher showed up to acknowledge the madness and even Shy Ronnie busted some rhymes.