flag
1. verb, slang To arrest someone. The police will flag all of us if they catch us drinking—we are underage, you know.
2. verb, slang To fail something. You better study hard, or you'll flag this exam.
3. noun, slang The grade of F on something. You better study hard or you'll get a flag on this exam.
4. noun, slang A bandana worn to show one's gang affiliation. What color flag is that kid wearing?