Seth is gay.
Nearly half of all his dialogue is "Have I Mentioned I Am Heterosexual Today?
" and is insanely jealous when Evan spends time with anyone other than him. And then when he carries him home...
The cops are Seth and Evan from the future.
They've come into the past to help guide the three main characters in a coming of age story, as well as helping to strengthen Seth and Evan's friendship (particularly notable when they forces Seth and Evan to hold hands).
If Jimmy's brother had been onscreen, he would have been portrayed by Jesse Eisenberg
Because people believe that he and Michael Cera