It's one of his most famously bizarre moments -- Tom Cruise jumping up and down on Oprah's couch ... on national TV -- but surprisingly, the big O doesn't think the outburst had ANY effect on his marriage.
Oprah was out in DC yesterday, when she was asked if Tom's infamous 2005 couch stunt damaged his relationship with Katie Holmes -- and she burst out laughing ... calling the mere notion "ridiculous."
In case you forgot, Tom had been dating Katie just over a month at the time ... and exploded on Oprah's show, explaining how head-over-heels he was about his new girl.
But here's the thing -- the incident is widely cited as evidence that Scientology had fundamentally changed Tom Cruise ... for the worse ... so it's not crazy to wonder if Katie saw red flags from the get go.
You gotta watch the clip -- Oprah's reaction is hilarious ... even Gayle gets involved.