Doug H in comments at RealClimate:
Mel Blanc's epitaph (and epithet - click through to see why), Steve of Upland image; some epitaphs fit better than others
Humanity’s epitaph:
- Not Dead. Resting. (with apologies to Monty Python)
- I told you we should have evolved faster.
- We’ve all gone to Hell – it’s cooler there.
- The meek inherited the Earth they deserved.
- I hear Venus is pleasant at this time of year.
- So long, and thanks for all the fossils.
- So much plant food, so few plants . . .
- Look on our works, Ye mighty, and despair.
Millard Fillmore's Bathtub 
Hey look. There’s a thin layer of mercury atoms in all the sedimentary rock right before the great extinction.
LikeLike