Johnny Knoxville in Jackass. Image via Paramount Pictures It feels weird to think of Jackass, the TV show and movie franchise that can be best summed up as " Johnny Knoxville and his friends injure themselves grievously for fun and profit ," as a cultural institution. It's been around for decades, though, and its DNA can still be seen in every YouTube prankster kicking around today. Knoxville seems aware of this, and the upcoming umpteenth Jackass movie, best and last , is billed as a grand finish to a long and painful career . Again, as if Jackass — the franchise revolving around Knoxville getting tased in the balls — is deserving of a warm, wistful finish. Granted, you can't get tased in the balls forever. Knoxville is in spitting distance of sixty, after all, and the next spill could always be the one that kills him. Somehow, though, I get the feeling that if anyone is going to be doing this for an entire lifetime, it's probably him. I can't wait to see Jackass: One More, Actually when he's eighty.…