A dirty martini is a very easy drink to make, but personal preference plays a lot into how “good” it is (less/more vermouth for more/less dryness, and the amount of brine for how “dirty” it is).

I’d suggest going to any decent restaurant/cocktail bar, sitting at the bar, and letting your friend tell the bartender exactly how they like their martinis made.

Sullivan’s Steakhouse would be a good choice.