Watch science comedian Brian Malow here and here. Just an example from his repertoire of bar jokes:
Some helium gas drifts into a bar. The bartender says, "We don't serve noble gases in this bar." The helium doesn't react.
What a gas! Malow's jokes I mean.
And to add to his wonderful collection here's my own contribution:
A DNA molecule walks into a bar. The bartender says, "We don't serve double helices in this bar." The DNA immediately turns around and splits.