How close can i make a parody of a song?

me and my friends want to make a parody of Pit bulls song give me everything about call of duty. (disregarding the fact we are nerds) how close can i make the parody lyrics to the song without getting copy writting. oviousley its going to be very different because of the subject matter but should i make a point not to use any of the regualr words they do in a stanza of the song? any other advice is good