Play video content TMZ.com Nick Cannon was in the house to see his ex-wife Mariah Carey leave her mark on Rihanna‘s breast … and he says more women should follow their lead. We got Nick heading in to do some charity work Friday at the Los Angeles Mission and our photog asked him about the viral video from Mariah’s recent concert. Play video content Nick says watching Mariah autograph RiRi’s boob was “hot” … and...