Given the type of environment you are exposed to while at certain restaurants that feature women wearing hardly any clothes, is it a sin to eat there?
If someone had to eat out and had no other known choice of restaurants (e.g., travelling in a strange location and unsure that one will be able to find another restaurant within reasonable driving distance), it would not be wrong to go into the restaurant to eat. If anything can be done to avoid prolonging the stay (e.g., ordering the food to go), that should be considered. Also, if one needed something else but had no other reasonable options for obtaining it (e.g., to use the phone or a restroom), one could go into the restaurant for that reason.
But if one has other choices, why would one choose to patronize an establishment that considers the immodest display of women’s bodies to be entertaining for the customers? Not only is the person being presented with immodest displays by service personnel, but proprietors and clientele that consider such display a commodity that can be bought and sold are likely to contribute to an overall immodest atmosphere.