Former WWE wrestler X-Pac -- who co-starred with Chyna in their 2004 sex-tape -- says he absolutely refuses to watch her new XXX flick ... telling TMZ "It's too hard remembering how devastated she was the first time around." 



TMZ spoke with X-Pac -- real name Sean Waltman -- who tells us, "It saddens me ... but she obviously hasn't progressed very far in life."

As we first reported, Chyna recently struck a deal with Vivid Entertainment to release a brand new porno flick featuring the former Playboy model in some compromising positions with multiple endowed male professionals.

Sean adds, "[Chyna] used to say how low she felt after the first [sex tape] was released ... what does that say about where she's at in life now?"