"Yeah. Annie's the one who went mad when her district partner got beheaded."
The District 4 Male was the male tribute from District 4 participating in The 70th Hunger Games, meaning that he was Annie's district partner.
During halfway of the Games, he and Annie decided to side with the careers. When they tried to leave, one of the career pack, the District 1 Male, beheaded him, traumatizing Annie. This was probably because they either had a good relationship with each other, or the beheading itself horrified Annie. Of course, it could have been both. After this incident, Annie went insane from witnessing the massive trauma she experienced.