Assuming that you are trying to attract male customers to your salon (rather than trying to get them to, for example, buy gift certificates for their significant others), you will need to make an ad that argues that going to a nail salon can be masculine. One possibility would be to get a very masculine celebrity and have him say that he gets manicures. Another possibility would be to have some sort of an ad that would imply that women are more attracted to men who have hands that are strong and manly but also neat and clean. Either of these might help to persuade men that they can go to nail salons without compromising their masculinity.
Men have been getting manicures for many years and are still getting manicures in some upscale barber shops. Typically the manicurist will do her work while the barber is cutting the customer's hair. There is nothing terribly embarrassing for a man about getting a manicure--but what men would balk at would be going into one of these contemporary nail salons where the atmosphere is as feminine as that of a beauty parlor and where all the customers are women. The customers are not only getting their fingernails manicured and painted, but they are having their toenails given the same treatment, and in many cases they are having their lower legs waxed to remove hair. There are even other feminine services offered, such as eyebrow waxing or trimming and even bikini waxing!!! This is obviously a place that specializes in services for ladies. Most men would feel conspicuous and out of place there. And they might even suspect that the women customers would resent their intrusion. It would be extremely difficult to overcome men's natural reluctance to patronize such an establishment. And if a nail salon started catering to male customers on any significant scale they might lose some of their female customers, who are much more lucrative because they consume more services.
I believe the only conceivable approach would be to get some men to start actually patronizing these salons either by paying them to act as shills or by offering coupons that would entitle them to free manicures. It would have to be done on a trial basis to see how the female customers would react. I suspect that many women would regard it as an invasion of privacy--but the times are changing.