When I was a teenager, it was legitimately obnoxious stuff like “daddy would you like some sausage?” and the WWE (then WWF) “suck it” gesture. I find 67 a lot less annoying in comparison–it’s basically just 69 but without the hypersexual fixation behind it. And “let’s go”/“LFG” is just an exclamation of joy or satisfaction like “yes”/“fuck yeah”.