it means to celebrate a friends negative forthcomings or pain filled situations or to be intrigued by a stoners random rants on life,cars that run on water, etc.
"dude i just took a shit that took away my manhood" "indubious!!" "dude theres this car that runs on water" a car that runs on water? indubious!
A differentway of saying certainly or of course, however, it is funnier and makes you look smarter. The word's origin is unclear, however, it is speculated it started in the comedic movie "seven days in hell". After its appearance in this movie, the word supposedly gained popularity in East China, to finally spread worldwide.
A random white boi: Is your girlfriendcute?
Mr. Chen: Indubdiously not