How do you measure an actor's greatness? You watch how he uses his instrument, that unique gift he wields to make magic onscreen. For Sir John Gielgud, it was his magisterial voice. For Christian Bale, it's his shape-shifting body. For Keanu Reeves, it's his endlessly expressive face.

And for Seth Rogen, whose latest surefire blockbuster, Funny People, comes out today? It's his T-shirts.

Yes, few realize that behind Seth Rogen's rise from supporting player on Freaks and Geeks to toplining, multi-million-dollar–movie star is a collection of expertly-curated T-shirts, each one of which — through a delicate balance of sincerity and irony, washedness and unwashedness — has driven his performances to heights he might never have reached on his own. From bands Seth Rogen's character likes to bands he likes ironically, from Los Angeles chicken restaurants to fictional TV shows, the T-shirts of Seth Rogen have stories to tell.

We've culled through hours of footage to find the greatest T-shirts of Seth Rogen's career. And we've tested every one on our patented Iron-i-Meter™, which measures how ironic each shirt is* on a scale of 1 (say, a Nirvana shirt) to 10 ("Wisconsin: Smell Our Dairy Air"). How has Seth Rogen grown as an actor and an artist over the past fourteen years? His shirts tell the tale.

*This is not to be confused with the Iron-o-Meter™, which measures how frequently the shirt in question has been ironed. All of Seth's shirts received a 0 on the Iron-o-Meter.