The VATRY, LIFFY, BOYNE and TOLKA fixes off the east coast on the border of the Irish-London FIR are named after the rivers Vartry, Liffey, Boyne and Tolka which all flow into the Irish Sea. The Vartry one is stretching credability a bit as its much further south than the river's mouth which flows out through Wicklow town. The Vatry SID though does pass over this point, more or less.
This is all my personal theory but it seems to fit the facts.
The other SIDs are also named after the navaid/fix that they terminate at, though how some of the other fixes got their names I couldn't guess.
I think just about every five letter word (including ones that will amuse children of all ages) is used for a fix code somewhere in the world and there's many duplicates.