Kanye West and his "wife" Bianca Censori are banned for life from boarding a Venice boat company's vessels after the rapper flashed his bare butt on board.

The 46-year-old father-of-four was photographed with his pants down during a boat ride in Italy with his 28-year-old architectural designer other half - whom he married in a non-legally binding ceremony in January - and the boating firm has called out the pair for the obscene behaviour and banned them from ever boarding one of its boats again.

Venezia Turismo Motoscafi told Daily Mail Australia: “The driver had to keep a lookout for traffic and did not see these obscenities.

“If this had happened, he would have immediately disembarked and reported the transgressors to those in authority.”

A third person with the couple “obstructed the captain’s view” into the back of the boat.

They continued: “We completely dissociate ourselves from such acts and behaviour.

“Mr. West and his wife will certainly no longer be welcome on board our company’s boats.”

Controversial Kanye exposed his bare bum to tourists in neighbouring boats while riding the river taxi in Venice’s famed canals – while Bianca is regularly seen wearing revealing outfits.

And his ex-wife Kim Kardashian is said to be “desperately embarrassed and worried” by his pantless antics.

During his bottom-baring outing, Kanye was dressed head-to-toe in his signature black, while Bianca donned a leather trench coat with little to nothing under it.

A source told The Sun: “It’s hard for (Kim) because as soon as she thinks she can move on, something like this happens and she’s pulled back into it.

“It’s like every time Kanye and Bianca pull these nearly-naked stunts, it reminds everyone that Kim dressed up in skintight nude outfits during the marriage. She’d rather put it behind her and forget about it.”

Kim and Kanye have been co-parenting sons Saint, seven, and Psalm, four, as well as daughters North, 10, and Chicago, five, since their split.

The 'Jesus Walks' rapper and Bianca got “hitched” two months after his divorce from Kim was finalised.