Bill Belichick has reached his boiling point in the Antonio Brown saga ... abruptly ending a press conference after reporters peppered him with Qs about his controversial superstar WR.

The New England Patriots coach faced the media on Friday -- just hours after the NFL opened an investigation into alleged texts Brown sent to a woman accusing him of sexual misconduct in 2017.

Of course, the media wanted answers ... but Belichick told reporters right off the bat he wouldn't be answering any questions about AB. He opened saying, "We take all situations with our team very seriously."

"There's some things we're looking into. But, I'm not going to have any comment on any of the off the field situations or questions on that."