Spotted **** - especially home-made (and with custard) is so delicious and well-loved, it triumphs over any shortcomings over its name!
re: "King ****", my take on the name is only very slightly different from Flange's
It's not a brand that is normally seen outside of serious-use circles (at least not in the South-East)
Some may think it''s slightly amusing but I wouldn't call it a double-entendre. **** has so many slang meanings (even are many are derived from the same thing) but I've never heard King used in connection with it used instead of ****, knob, willy or more crude terms. Young guys may laugh at it once but they'd be though of as pretty gormless if they saw it as a long-running joke.
Older folks would think, instantly (if at all) of a reference to one our Kings Richard, particularly the Third (who was character-assassinated by Shakespeare, presumably at the behest of some sponsor).
So, on balance i'd said no - if it is seen as a "saucy" joke, it's too mild to pass muster. Someone who's being a bigger-********-than-most might possibly be called a Prize **** but not a King **** - but then I'm only guessing at what the connotations might be Stateside...