You get the last word...

[RBeckman]

Although widely disapproved as nonstandard and more common in the habitual speech of the less educated, ain't in senses 1 and 2 is flourishing in American English. It is used in both speech and writing to catch attention and to gain emphasis <the wackiness of movies, once so deliciously amusing, ain't funny anymore — Richard Schickel> <I am telling you—there ain't going to be any blackmail — R. M. Nixon>. It is used especially in journalistic prose as part of a consistently informal style <the creative process ain't easy — Mike Royko>. This informal ain't is commonly distinguished from habitual ain't by its frequent occurrence in fixed constructions and phrases <well—class it ain't — Cleveland Amory> <for money? say it ain't so, Jimmy! — Andy Rooney> <you ain't seen nothing yet> <that ain't hay> <two out of three ain't bad> <if it ain't broke, don't fix it>. In fiction ain't is used for purposes of characterization; in familiar correspondence it tends to be the mark of a warm personal friendship. It is also used for metrical reasons in popular songs <Ain't She Sweet> <It Ain't Necessarily So>. Our evidence shows British use to be much the same as American.