Would smiling be a proper response when someone insults you ?

Could be. There are others, maybe, that may fit the situation better. If you're quick-witted, you might find one insult to hurl back instead.  Or maybe just turn and walk away. Hitting would be the ultimate and last choice.

Better response is to ignore the person who insults you. Smiling is not a bad idea it gives the impression to the person who is insulting that the other party just do not care about his insults . He will get disgusted . 

I prefer the short response........"someone pee'd in your mother"  and then turning on your heels and walking away. 

It would certainty be a surprise reaction to a insult or you can also add a little chuckle to the smile.

Watch the Ben Askren vs Jake Paul press conference. Ben will show you how to respond like a man to insults. 

You have to be careful if you do that.  It could really anger the person who insulted you.  It's best to just ignore them.

No the best response is no response when somebody insult you don't show them either a smile or a frown just let it fly right over your head like you didn't even hear it.

Me I usually will very quickly invent an excuse to be gone when somebody starts insulting me . You can put a shortcut to a ringtone on your telephone desktop and just touch it and it'll make your phone ring.

You tell the person that's insulting you I've got a call I got to go see you later as you're walking away.

It depends on the insult! Most of the time it's better to have a snappy come-back to shut them up, so you don't start something you don't want  - being insulted all the time -"I'm just joking, why are you so sensitive?"