An extra-meaningful word similar to "slander".
"People like to run smear campaigns about the Bush Administration.....you'll also see LOTS of smear campaigns in high school."
A bowel movement that leaves considerable feces stains on the toilet bowl. Specifically one so repulsive that others will not want to use the toilet afterwards.
Dude, I'm just gonna piss in your laundry tub. Jeff ran a nasty smear campaign on your toilet and I can't stand to look at it.