I saw a trailer for a soon to be released movie I'd really like to see called "Cyrus." It seems like it deals with the nightmares of dealing with an adult stepchild. The two "parents" are played by John C. Reilly and Marissa Tomei and the stepkid is that chubby guy from Superbad. From what I gathered from the trailer it seems to be done in a comical, yet real and touching way. Sort of like "The Squid and the Whale" which if you haven't seen that - it's an awesome look at a marriage with children that breaks up and how they all deal with it. The dad is a total narcissist and he's PASing mom before they even split. But I digress ...

Here's the plot summary for Cyrus from imdb:

With John's social life at a standstill and his ex-wife about to get remarried, a down on his luck divorcée finally meets the woman of his dreams, only to discover she has another man in her life - her son. Still single seven years after the breakup of his marriage, John has all but given up on romance. But at the urging of his ex-wife and best friend Jamie, John grudgingly agrees to join her and her fiancé Tim at a party. To his and everyone else's surprise, he actually manages to meet someone: the gorgeous and spirited Molly. Their chemistry is immediate. The relationship takes off quickly but Molly is oddly reluctant to take the relationship beyond John's house. Perplexed, he follows her home and discovers the other man in Molly's life: her son, Cyrus. A 21-year-old new age musician, Cyrus is his mom's best friend and shares an unconventional relationship with her. Cyrus will go to any lengths to protect Molly and is definitely not ready to share her with anyone, especially John. Before long, the two are locked in a battle of wits for the woman they both love-and it appears only one man can be left standing when it's over. Written by Fox Searchlight