Washington Wizards baller Kelly Oubre is setting the record straight -- saying he's "NOT a lesbian" ... despite what some fans say.

The 21-year-old rising star was talking to CSN Mid Atlantic about some of the crap he gets from opposing fans ... and dropped this shocker. 

"People call me a lesbian a lot. They think I look like a female girl or a teenage girl or something."

So, why the lesbian jabs? Oubre says he thinks he knows why ... 

"I understand I'm a pretty dude. They might be mad that their wife likes me or something."

But to be clear -- "I'm not a lesbian. I'm a grown man."

"I've heard that multiple times. I guess it's something to try to get under my skin, but at the end of the day I know who I am."

And now you know.