How do you politely ask the homeless to stop touching your babies?

Thanks to the wonderful people at Baby Bjorn, Laurin and I have been taking the ladies for a lot of walks lately.   It was really nice out yesterday, so we hardly had to bundle them up.  While walking is fun for the whole family, having two amazingly cute babies strapped to you makes you very popular with all kinds of people.  It seemed like everyone was out and about yesterday, and they all love babies (especially twins).   Our most exciting encounter came when we came across two colorful characters enjoying some time out on a nice day.  As we walked up, the man was putting his forty of Cobra back in his windbreaker, and the woman must have just finished putting bright red lipstick all over her face and teeth.  It seems like the twins thing really intrigues people.  We almost made it past them, then I hear "TWINS?!?!?".   Not wanting to be total elitists we were forced to stop and acknowledge them.  What ensued was a 10 minute session of confusing conversation and fear of hepatitis.   The guy focused on me, telling me the story of his son, who is apparently an extra in movies (he was one of the cops that found Jimmy Hoffa's body in Bruce Almighty he said).   He also rambled about how great our girls will be and how they need to know their real father, the Lord.   Laurin's conversation was apparenly about the fact that the woman had 6 kids.  Where they were was anybody's guess.  One was 3 months old.   She showed Laurin a photo on her camera, then took a photo of Riley.  There was some awkward touching and at one point the woman put Riley's pacifier in her mouth.  Im not sure if they make water hot enough to clean it, so I think we retired that one.   I tried multiple times to end the conversation, but apparently they didnt major in getting hints.   Finally we used their impending hunger as a reason to move along.  Fun times.  I actually found the guys son online.  He seems pretty successful and together.