My best friend (from 19 years old) moved back to Hawaii (and in with us for the first few months)when my son was 4.5 and hers was 5. The boys had different personalities and it was hard after the first "honeymoon" week. The good thing is that by being together they both advanced in different ways. My son is outgoing, playful - loves rough play, talkative, energenic. Her son was much more quiet and introverted, did NOT like rough play and very whiny. So everyday, my son would irritate him and then the other would whine (very loudly) about it. THAT was annoying on both ends. My son had to learn to be more sensitive to what other people want to do or play (and sometimes to give people space) and her son did learn to be more outgoing and playful with enough time & encouragement. She worked on no longer "babying" her 5-year-old and I worked on my son as well. We talk & compare notes about what they said about the other and soon learned what worked well and what didn't. Most of all, I think it's helpful to talk to your friend about it and let her know that you recognize that your son is being rude and you want to work on that. There should be a consequence if your son is rude to anyone. Also, her son might need to realize that yours may not always feel like playing and it's okay to do solo activities (puzzles or something). We made it clear that they had to get along because they were going to grow up together (more like cousins). When they both got GameBoy games, they completely bonded by sharing the "cheats" to get to higher levels and had entire conversations that we didn't understand. They borrowed each others games and traded games, etc. We just kind of let them work on their relationship naturally and just kept getting together and they worked it out. Sometimes if mine made her son mad, I'd talk to mine about it and we worked on that. As they've gotten older, they've developed more and more common ground and respect each others differences and have learned to meet in the middle - such an important life lesson. They are 11 and 12 now. I hope it works out for your boys as well.