The following are in no particular order of importance.  This is just a very short list of offensive web site practices.  For a more detailed list, see the page from WebSitesThatSuck.com. Many thanks to them for providing this information.

Your site says “Welcome to…” on the home page.

Your site mixes text colors on the page.

Your SITE USES LOTS OF WORDS IN ALL CAPS.

Your site has anything that blinks or objects that move or fade.

The Comic Sans font appears anywhere.

There is no obvious way to get back to the Home page from other pages.

Scrolling left/right is required to see the entire page.

Your site uses text that is centered in any place other than headlines.

Your site uses justified text.

Your site has any dead links.

You have misspelled words or poor grammar (your vs you’re, there vs their, etc.)

Your site uses clipart.

Your site uses animated GIFs.