I wasn't even playing when I fell out (permanently so far) with an old friend at a session. Another guy was doing a very sensitive, slow solo on the fiddle. My friend (drop taken) joined in, "improvising" loudly with respect to none of tempo, rhytm nor melodic structure. I asked him to stop, he threw a huge wobbly that ended up with him threatening to hit me. That was over a year ago, I haven't seen him since.