Can a business kick you out of their establishment for kissing your girlfriend?

My sister and her husband were at a comedy club with their two friends. The girls kissed each other one time (not making out, not , just one small kiss), then this big black bouncer came over and said to them, "Let's keep it straight up." And proceeded to kick the whole group out of the club. My sister got the managers involved, but they sided with the bouncers and began cursing at my sister and her friends and calling the partners all kinds of filthy, hateful, phobic names. Is it legal for them to kick out paying customers simply for being s?? My sister would like to know if they have grounds for a lawsuit.