Charlie Day’s love of romantic comedies started long before he was cast to lead one. The Manhattan-born “It’s Always Sunny in Philadelphia” star couldn’t wait to tackle the genre when his new movie, “I Want You Back,” came along, citing an affinity for classics like “Sleepless in Seattle” and “When Harry Met Sally.” “I really love Tom Hanks and Billy Crystal,” Day told the Daily News. “To get to see them be leading men in movies, but also leading men in an attainable and familiar way — they have this sort of everyman feel. I was hopeful that I’d one day get an opportunity to do my version of t…