Continuity mistake: It is stated that Phil and Claire didn't have a wedding, and just went to the courthouse to get married, but in episode 1x08, Great Expectations, Phil says he's pretty sure he sang "If you leave" by O.M.D. at their wedding.
Continuity mistake: When Haley, Claire, Phil and Jay are by the pool and Claire is talking to Phil. Claire's shirt (cover up) changes position several times. (00:02:00)
Answer: Mitch is upset that his dad doesn't seem to support his getting married. When they talk about Jay's friends not coming to the wedding, Jay makes it seem like Mitch wouldn't want them to come anyways. Mitch sees it as it's actually that Jay doesn't want to invite his friends to his gay son's wedding because he's embarrassed and uncomfortable about having a gay son. Essentially Mitch sees it as if he was marrying a woman, Jay would be willing so spend money on the wedding, host it at the club, and invite all his friends to it.
Bishop73