I have a son with autism, and rather than try to explain aspergers, I have had better luck explaining that sometimes family members also have "autistic-like traits".
Something I found interesting and somewhat amusing -- my son and I were waiting for a meeting in a building in which a variety of organizations hold meetings. While waiting for our meeting, I walked over and looked at a poster for an Autistic Adult Support Group. While I was reading it, a small cluster of people walked up to me, and a twenty-something young man said to me, "Excuse me, are you looking for the Autistic Support Group?" I said no, but that I was reading it because of my son (I wasn't ready for the group I was meeting with to know my diagnosis). Not fooled, the young man looked at me and said, "We can usually pick out own out of a crowd." Indeed!