I came up with a few ideas of how you can wear a diaper on halloween and not just be the generic baby costume:
-Toddlers & Tiaras: You wear a fancy dress, a crap ton of make up, a sash (saying beauty queen or something), a paci, a diaper
-Rugrats: Dress up as Tommy, Chuckie, Phil & Lil or something!
-Baby New Year: Top hat, Sash saying 'happy new year', diaper
-Stewie from family guy: yellow shirt, red overalls, diaper
w0o0o00ooooooooo fun, if you have more ideas, feel free to add them