Kids who make fun of or pick on Handicap kids. That's about as fucking low as you can get.
There was this kid at my high school who would always pick up change off the ground so these kids would get like 500 pennies and just throw them at him or they would get a bunch of change and super glue it to the ground so he couldn't pick them up. He'd come back and try literally every 5 minutes and these freshman punks just laughed their asses off.
After about a week, some seniors kicked their asses. The administration got involved and gave the seniors a detention or something but suspended the Freshman kids for a week. Some kids parents even thanked the seniors for teaching his kid a lesson.