What is some British slang that Americans tend to not know about?

[Benjemin]

Mardy = annoyed and/or miserable - mostly a northern expression. Also, until very recently, pissed always meant intoxicated, pissed off meant irritated, annoyed. Occasionally now I hear pissed used in the American way. Arse = ass (as in backside), e.g. a pain in the arse, don't be an arsehole, etc. Fanny = general female genital area, which is why we might giggle at the idea of a fanny pack. Randy = horny. Bum = backside (not even a vulgar word, small children sometimes call their backside their bum) Hopefully this will help explain why the name Randy Bumgardner is especially funny here. Also Fag = cigarette, again, not an especially vulgar word. (Also tabs=cigarettes in the north-east.) E.g. 'I'm going outside for a fag' = I'm taking a smoke break.

[Teresty]

Thanks for explaining these expressions , slang can indeed vary greatly from region to region and if you are interested in learning more about modern slang words and their meanings, I would recommend check this web site (https://slang.parentaler.com/slang/function-or-func-meaning/), a great resource for understanding different slang terms and it will help you get a better understanding of colloquialisms.

[Billie34]

This is something that needs to be paid attention to when using words to avoid Webfishing (https://webfishinggame.io) situations where it becomes an unwanted meaning.