George and Amal Clooney have reached a milestone -- their 5-year anniversary -- and it seems their key to a happy marriage ... is finding joy in the difficult stuff.
The couple was leaving 4 Charles Prime Rib restaurant in NYC Thursday night on the eve of their big day, and we asked what the hardest part of being married is after half a decade ... and they were VERY amused.
It's hard to tell what's so funny exactly -- the question itself or the possible answers. Truth is, George and Amal both manage high-profile careers while also raising 2-year-old twins ... so maybe it's just humorous trying to narrow it down.
BTW, the Clooneys were joined at dinner by another high-profile couple -- best friends Cindy Crawford and her hubby, Rande Gerber, George's partner at Casamigos Tequila.
And, not that any of them need it, but if they're looking for marriage advice ... Ruth Bader Ginsburg recently shared what she told another famous couple about to tie the knot -- J Lo and A-Rod -- and it makes perfect sense.