ribald
Meaning: coarsely, crudely humorous
Usage: The ribald joke was too crude for the school assembly.
scurrilous
Meaning: grossly abusive, vulgar, or slanderous
Usage: When Bruno heard the scurrilous accusation being made about him, he could not believe it because he always tried to be nice to everyone.
obscene
Meaning: offensive, indecent, or morally objectionable
Usage: The school removed the obscene graffiti from the wall before classes began.
vulgar
Meaning: crude, indecent, or lacking refinement
Usage: The teacher reminded students to avoid vulgar jokes during the assembly.