Bust a cap in his ass: African-American slang. “Bust a cap” means to shoot (a cap can be a small explosive used to set off a larger explosive, especially in mining, so in slang, it’s a bullet); one’s ass can be used as an emphatic replacement for a pronoun: “my ass is tired”, “he has to drag his ass to work”. Possibly from work one’s ass off (to work to the point of fatigue).

Yardie: a Jamaican (“yard” in Jamaican Creole means “home”); more specifically, a member of a Jamaican gang

Goody gumdrops (or goody goody gumdrops): childish expression of happiness, usually sarcastic when used by adults.

Pisshead: person who regularly gets drunk. “Piss” can be used to mean alcohol (“We’re going on the piss” = “we’re going drinking”); -head can be used to form a noun (usually derogatory) for a person who’s dedicated to something: a pothead likes to smoke marijuana (“pot”), a metalhead listens to heavy metal; it can also be added to other insults to imply stupidity (blockhead, shithead).

Look like curry to a pisshead: curry is an extremely popular post-pub food in Britain, so this is irresistible food.

Porky pies: rhyming slang for lies. Usually shortened to porkies.