Smiles are contagious . . . Be a carrier.
Humour aside, if you smile at someone they invariably relax and smile back. Of course, there are the hard cases, but even those tend to thaw if you persist in interacting with them in a positive manner.
There are lots of old age homes in my area and I come across many old people on a regular basis. I always try to find time for them as I think I might be the only person they speak to that day. Also, I seem to have the kind of face that encourages a complete stranger to tell me their life story in the fresh produce aisle!
I am a firm believer in being pleasant and polite. You will get much farther in life than being rude and demanding. It’s the carrot or the stick approach and I have never seen the stick work!