Continuity mistake: In the scene when Galahad is taking Eggsy below ground at the Kingsman Tailor Shop, they enter the dressing room and the door is open with it still open in the mirror in the next shot. Then when they go below ground it is magically closed.
Continuity mistake: When Eggsy is in the interview room at the police station, in a wide shot the tape recorder is on the table by itself, with nothing around it. Eggsy demands a phonecall, the police officer leaves, and Eggsy then reaches beside the recorder and picks up a cordless phone which has appeared from nowhere. (00:16:45)
Continuity mistake: When Eggsy meets fellow cadets and one of them asks if he's served him in McDonald's, in one shot, Eggsy folds his arm before replying, and then in another, does the same again, from a different angle, while replying. (00:31:45)
Continuity mistake: Near the beginning, as Harry gently takes the snowglobe from Eggsy, in the shot of Eggsy the snow is relatively calm, then in the immediate reverse angle as Harry looks at it, the snow is instantly shaken up.
Continuity mistake: When Eggsy and Harry are walking toward the Kingsman tailors just before he gets introduced to the new weapons, there is a long shot of them walking down the street and two silver cars are coming down the street behind them. In the next shot the two silver cars that should still be in the background have disappeared. Also, as they approach the Lexus parked in front of the Tailor's, and there is no car beside them, in a second perspective, there is suddenly a black vehicle parked behind the Lexus.
Continuity mistake: Just before the bar brawl, Harry takes the time to lock and bolt every exit and doors so that there would be no possible escape from his wrath...after all is done, and he is done kicking ass he proudly walks away and right through the front door without unlocking it.
Continuity mistake: In the end credits scene, when Eggsy appears in the pub, Dean is holding a pint glass in his hand, but in the next shot, the glass is suddenly on the table.
Continuity mistake: At the start, the way Harry holds the medal of valor changes between shots. (00:03:20)
Continuity mistake: When Valentine is speaking with Princess Tilde through the prison door, his position changes during the reverse shots from Tilde's perspective. On his side of the door, his left shoulder is closer to the door, but in the reverse shot, his right shoulder is closer.
Continuity mistake: After the church massacre, you can see a row of jackets hanging next to a Confederate flag. When the shot changes, the jackets disappear. Then the shot changes again, and the jackets reappear.
Continuity mistake: When Harry and Eggsy are talking about the newspaper headlines, in Harry's study, once Eggsy sits down, the desk lamp on Harry's desk rotates between shots, the main boom arm also changes angles from vertical to set on an angle.
Continuity mistake: In the pub fight, when Galahad stuns the last thug, you see Eggsy flinch and start to move back, but when the shot changes he's sitting back up perfectly still as if he hadn't moved.
Answer: Details aren't given, but it seems that Dean is involved in local crime along with the gang that hangs around with him. Even if Harry is bluffing, and doesn't have specific proof, it is clear that he is abusive and he has the recording of him threatening Eggsy.