1> All time greatest achievement Indoor plumbing.

2> 20th Century's greatest achievement Women's rights and the decrease in sexism, racism and inequality. We still have a long way to go, though.

3> So far the greatest achievement of 21st Century The internet--as a means of instant transfer of information and ideas.

4> All time worst achievement: Murder.

5> 20th Century's worst achievement Holocaust

6> So far the worst achievement of 21st Century The "Snuggie". It's so annoying. >_> They're robes. Buy a gosh darn robe!