In my 41 yrs, have never seen anyone called out for high fiving the first base coach, but if he/she ran out of the base line before hitting bag to do his/her high fiveing I guess in theory they would be out, but have never seen it.

That's a good question, There is a rule about coaches assisting a runner. Some leagues have been known to go overboard with the rule and prohibit any contact with the coach. It is best to check with your league to see how they enforce this rule.

I've heard that a player was called out in a game I was not in, I've witnessed a player and one of his teammates being admonished by the umpire, most are just let go and let the kids enjoy a good hit.

Without looking it up in our rule book, I believe the absolute wording is that the player will be called out. Although I never seen it enforced.....