They are more often than not incredibly loud, rude and lack almost all basic human courtesy we take for granted in the west and even in asian countries like Thailand. They will push past you in queues, yell mandarin loudly in your face to others behind you, stand in the middle of the street blocking traffic, play videos on their phone speaker on full volume without using headphones - I could go on and on and on.
There's absolutely zero consideration for anyone but themselves and are, by a wide margin, the rudest tourists i've ever encountered anywhere.
I can't help but wonder if it's just the type Chinese tourists that visit Thailand and mainland China would be different, but its just not a risk i'm willing to take.