Lady just cut my boyfriend off in the far left lane if I-25; literally pulled into him as he was honking at her to let her know he was there. He had to slam on the brakes so that she wouldn't drive into his front end. This was after he pulled into the left hand lane to pass her bc she was driving under the speed limit. She then continued to drive 5 miles under the posted speed limit in the passing lane, and we were unable to go around her. Once we were able to merge right, she sped up.