really was.The off-Broadway cuckoo camp-fest at the Asylum in Chelsea is, by a nautical mile, the funniest musical in town right now and is built on an unsinkable idea: It tells the story of the 1997 movie “Titanic” using the songs of French-Canadian chanteuse Celine Dion. One hour, 40 minutes with no intermission. At Asylum NYC, 307 West 26th St.It’s scandaleux that no one has ever thought of this mashup before. After all, no singer is more closely tied to a (non-musical) movie of this scale than Celine is to James Cameron’s “Titanic” — the two feed off each other — and the rest of her popular catalog has the same emotional heft and theatrical narratives as the Oscar-winning film’s signature song “My Heart Will Go On.” And co-writers Marla Mindelle, Constantine Rousouli and Tye Blue cleverly toss in a boatload of ’em wherever they can.When Jack and Rose first meet on deck, as Rose is considering throwing herself overboard, they sing a duet of “Taking Chances.”“What do you say to taking chances? What do you say to jumping off the edge?” they go.