A mackeral is a word used in London and the surrounding countys to describe a wannabe gangsta. These are people who try to intimidate others by threatening them with gangster actions such as 'spraying them wiv their Ak's' or 'merking them with their mandem'. However, any attempt to do so would be futlye. The perpertrators are normally 'wastemanz' or 'hairdressers' who try to make themselves feel better by trying to act cool and hard.
Martyn: oi blud , call up yo' Peter Pandem, we gots bare beef wiv rob da hairdresser
Matt: aaww Allow bruv, that bredrin is a Mackeral. I slew manz like dat on da reg just fo jizzlez.
A small fat kid with a mullet with ice cream on his face
Jesse-"Did you see that kid?"
Matt-"Ya, what a Mokie"