Give him a break , his belly is probably full <| sep |> He maybe the king , but that doesn ' t mean he can do whatever he likes . He pushes those limits to be sure , but that ' s not the half of it . You act like the slap is the only thing Tyrion has done . That gif is just an entertaining way of showing their relationship . They hate each other . And as i pointed out before Joffrey killed people just for begging at the gates . He ' s a psychotic sadist . He knows he can get away with killing beggars at the gates so he does it without thinking . He doesn ' t know if he can get away with killing his uncle no man is as accursed as the kinslayer so it makes sense that he would pick the perfect time . During the battle . His uncle has already put together the defenses . In Joffrey ' s mind it probably makes no matter if they have Tyrion on their side or not . It ' s not like he thinks of Tyrion as much of a warrior . Also no one would be surprised if Tyrion died in the battle . Whoever put out the hit or if he was doing on his own accord the battle was definitely a prime opportunity to do it .