This is bad. Late again!! I'm going to earn myself the nickname 'king of tardiness' before long.
Literal
Bad [よ]. Again late is!! Soon-already tardiness-demon [gen-の] nickname [obj-を] take-[regrettably-てしまう].
遅刻魔 is a playful compound: 遅刻 ('being late') + 魔 ('demon, fiend, fanatic'). The 魔 suffix is extremely productive for nicknames — 怠け魔 ('lazybones'), 勉強魔 ('study fiend'), 殺人魔 ('serial killer'). 異名をとる is a fixed collocation 'to earn a nickname / alias.' はやくも ('soon, already') is a slightly literary adverb combining the emphatic も with the 'fast' root. ~てしまう again flags the regrettable completion.