http://comicbook.com/2015/07/27/vacation-review-the-funniest-movie-of-2015/

My favorite bit is this: "The best part of Vacation is its relevance to today's world. Unlike Trainwreck which appeals to a niche audience, or Pixels, where the humor caters to seasoned audiences, Vacation finds itself checking all the right boxes for the today's cinema-goers.".

If he mean Trainwreck is for niche audiences I guess he means "niche audience" = "people who have had sexual experiences and deal with everyday problems"