Len,
Self selection does work both ways.
You can go elsewhere if they demand you perform the unclever songs, or they can go elsewhere when they realize you won't. The first avoids a prudish reputation. (Although how much would that woman you mentioned really remember, eh?)
Another facet of this whole self-selection business is that if you only sing cleverly bawdy songs with lots of vague reference and double entendre, the crass class just won't get it. They'll see people of a different sort smiling and snickering softly, and realize they are simply in the wrong place. Well, at least that's what one hopes, anyhow.

As for spacing them out...
An interest group I was a member of once had a singing contest, and I had the great misfortune to sing a bawdy song. Clever, I had thought, but apparently not as clever as the guy who came before with a more well known bawdy song. Two in a row was in bad taste, and I came out looking like the one who had gone over the top.

I think the previous gentlemen's suggestion to use bawdy songs like bait on a hook is quite useful.

Good luck to you!

In harmony,
Su Rynas