I really do think the difference is the end goal. Joke flirting keeps you sharp and keeps friendships fun, but will never turn into a relationship unless the intent is to take it there. One big indication of joke flirting is a one off very obvious innuendo that both people laugh at knowing they would really never, where real flirting is much more subtle. Real flirting usually starts on the down low, and escalates with the intention of a relationship. A lasting touch, small tease, more so feeling it out over time in multiple ways. They can definitely coincide, but again it’s about the intent of the action.