"Real Housewives of Orange County" star Vicki Gunvalson's topless Instagram photo was inadvertent ... so she claims.
Vicki posted a photo Thursday AM, thanking Bravo TV for her Christmas Present -- a nice set of headphones.
In the Dept. of Obvious ... even a casual look at the pic reveals Vicki was naked when she pressed the red button. She, however, says she never saw her boobs before posting the photo.
Vicki tells us she was distracted, getting ready for work.
The question ... are you buying what she's selling?