I can relate to your experience. This happened to my ex-husband and I at a local chain sit down restaurant. The language was so offensive, and the hostess was involved in the conversation, so we didn't feel comfortable complaining.
The next day I wrote a letter to corporate headquarters detailing our experience, and stating our dis-satisfaction. We got a letter back from headquarters with vouchers for meals and huge apologies. Then we got a call from the store manager who offered more vouchers.
The vouchers for free food wasn't my goal in writing, but I know my point was received.
I hope you say something to the owners or the manager.