An expression that means "Excuse me, you are involved in matters that concern me, not you, so I would appreciate it if you would give me some space and let me do my thing." Basically when someone says get off my jock they want you to back the hell up and leave them alone because you are being nosey and getting involved in shit that has nothing to do with you. Get off my jock can also be used to ask someone to remove themselves from your penis (jock = penis). If someone is feeling on your dick without your permission, the proper phrase to use would be get off my jock. Another time where the phrase get off my jock would be appropriate is if someone is arguing with you and you prove them wrong you can yell "GET OFF MY JOCK!!!!" to be like "Yeah dumbass you were wrong I was right!!!"
Brendan: Who ya texting?!
Christian: My friend from Oklahoma...
Brendan: Oh cool... What's his name?
Christian: HER name is Chelsea...
Brendan: Oh cool is she hot? Where does she go to school? How did you meet her?
Christian: Brendan, get off my jock... It's none of your damn business