NFL bad ass Jeremy Shockey is a horrible teammate and an even worse person ... this according to a guy who would know ... former NY Giants wide receiver Amani Toomer.
Toomer -- who played with Shockey for 6 years in NY -- CRUSHED the tight end on his Twitter page this morning ... after Jeremy said he'd be open to returning to the Giants.
As our friends at ProFootballTalk.com pointed out ... Shockey left the Giants on really bad terms in 2008 ... insisting he would NEVER play for the team again.
Now, Toomer wants to make sure Shockey's kept to his word ... tweeting, "No!! Shockey ‘I will never play4 you again!’ he yelled at jerry Reese in 08. Let him keep his word. Bad teammate, worse person."
It's unclear why Toomer has so much anger towards his former teammate.
Shockey -- who played for the Carolina Panthers last season -- has yet to respond.