LeBron James is pissed off at how Browns fans reacted to Deshaun Watson getting carted off the field on Sunday ... saying it's "LAME [as f***]" to boo someone when they're injured.
The controversial Cleveland quarterback suffered a potential season-ending ailment right before halftime in the Browns' 21-14 loss to the Cincinnati Bengals ... and as he was being taken to the locker room, the home crowd released a mixture of cheers and jeers.
King James -- who has been on both sides of the spectrum with Ohioans thanks to his departure for the Miami Heat in 2010 -- clearly took issue with how Browns supporters reacted .