Lawford's Falling Out
Peter Lawford ended up falling out with the rat pack after his brother-in-law, John F. Kennedy, snubbed Sinatra. JFK started to favor Republican Bing Crosby when going out, and Sinatra didn't like the snub. Sinatra was mad enough that he ended up cutting out Lawford due to his familial ties.
Ad-Libbed Lines
Naturally, the rat pack thought they were absolutely hilarious. It comes as no surprise that they went and ad-libbed their lines during Ocean's 11. They thought that they were funnier than the script.