teddy bears picnic
If you go down in the woods today,
you're sure of a big surprise.
If you go down in the woods today,
you'd better close your eyes.
'Cause Mum and Dad,
are 'avin a shag,
and Uncle Bob,
is suckin' his knob,
and Aunty Mary's 'avin it off with Graaaandad.
Uncle Bob was probably sucking his own nob, what with Aunty Mary being occupied with Granddad.
written by Jo*n Che*tha*, approved by Log

The Wallington Variation:
'Cos Uncle Ross is having a toss
And Uncle Frank is having a wank
And Auntie Flo is having a go
With Gran-dad!
It's worth noting that it's nearly always the Auntie who gets it on with Grandad in these scenarios. Other possibilities include Uncle Jim having a rim, Auntie Irene flicking her bean, and of course Diana Rigg having a frig.
written by Mi*e *lexa*der, Jo* Blyt*, approved by Log

There's also Auntie Sue doing a poo whilst Uncle Jim kisses her quim.

Presumably Sue and Jim are German.
written by Ni*k Hu*t, approved by Phil