Anyone seen an old SNL skit called Cawfee Tawk, where Mike Myers, dressed as a women, hosted a talk show? Every once in a while s/he became vaclempt, and would throw out a topic to discuss. Tawk amongst yah-selves s/he would say, before collecting him/herself.
I keep a few topics for discussion in mind, for different situations (not directly from SNL, those were much funnier than my bio-geek stuff). Still, they are quite useful for breaking out of one of those awkward silences that can occur when a group of semi-strangers is talking together. I'll throw one out at a conference or at a bar, and think "Tawk amongst yah-selves". I usually like to sit back and listen, whether vaclempt or not.
If I am with a group of physiologists or evolutionists, I throw out this one:
Why has bioluminescence evolved SO many times in the marine environment, but almost never in freshwater environments?
Or, if you're more interested in one for a bar that includes someone other than a biologist -
Why are all the best rock bands British, but all the best individuals of rock n roll American?