Here is another Jack Ruby sighting that is most certainly false: that he attended the Murchison party the night before the assassination.
But, if you go to Ken Rahn's Jack Ruby timeline, it's got Ruby going to the Egyptian Lounge for steaks with friends on Thursday evening and then working at the Carousel Club until 2 AM. It doesn't even mention the Murchison party as a possibility, not even as a rumor.
Recall all the bigshots that were reportedly at that meeting: Johnson, Nixon, Hoover, etc. Why would Jack Ruby protect all those people? And how nervous would they all be knowing that Jack Ruby was sitting on that knowledge? At some point, don't you think he would have lost it and sung like a canary? There is no good reason to put any stock at all in this Ruby sighting.