1. It was originally a slang term used in Ireland to mean either a) "to steal" or b) "to throw".
2. It's also used as a pretty mild swear word in Ireland.
It's used a) to express that you're pissed off or b) to describe somebody who pissed you off.
It's not related to the word 'Fuck', and doesn't have any sexual undertones, so is acceptable for polite company.
3. The characters in the sit-com Father Ted made the use of 'Feck' more popular outside of Ireland, most noticeably in the United Kingdom.
Unlike what a lot of people think, the scriptwriters did NOT invent 'feck' to get past censors who didn't allow the word 'fuck'. In fact, 'feck' was used as a mild swear word LONG before Father Ted made it famous!
1. a) "They had fecked cash out of the rector's room." - from James Joyce's 'Portrait of the Artist as a Young Man'.
1. b) "He asked me for a loan of my basketball, so I fecked it across the yard to him."
2. a) Priest: "Ah, feck! I left my keys at home."
Polite Ladies: "That's an awful shame."
2. b). "That bouncer was a right old fecker for not letting us in."