EXCLUSIVE

Amanda Bynes was unceremoniously ejected from a Ritz-Carlton in NYC Thursday after allegedly smoking weed in her hotel room and being so rude to hotel staff ... she made one poor girl cry ...sources tell TMZ.

Amanda begs to differ, telling us she left the hotel voluntarily -- and does NOT smoke weed.

Our sources say Amanda was a nightmare from the get-go, smoking weed everyday despite warnings from hotel staff. We're told Amanda tried using spray chemicals to mask the weed smell.

But that's not it ... we're told Amanda was unspeakably rude to the hotel staff, telling the front desk girl she was "too ugly" to check her in. We're told Amanda then offered her plastic surgeon's services to the desk girl in question ... and the tears started flowing.

The bad behavior continued until Thursday .... Amanda was scheduled to check out at noon, but the hotel staff had had enough ... and kicked her out several hours before mandatory check out.