When Debbie is looking at Matty's wallet, she is surprised to learn he's 20. However, his birth date is in 1991, which in 2014 would make him 23.
When Kev is in the hospital praising his magic penis, you can see the last nurse breaking.
When Carl is asking Lip about his blood type, he reveals that he's AB. When he tests Frank's blood type, the results show that he's O+. Even though we don't know Monica's, it is impossible for an O+ parent to have an AB child.