The act of Fiddlefucking can mean a number of things.
1Wasting time
2Messing with something (attempting to fix something, mainly hands on)
3Performing certain sexual acts on such female.
1 Bob! Quit fiddlefucking around and lets go!
2 Im taking my car to the shop, Im tired of fiddlefucking with the spark-plugs.
3 Dude! I was so fiddlefucking Sally in the back seat of your car!
An insult. Doesnt really mean much, though one can assume the person you accuse of being a fiddlefucker infact has sex with fiddles. The Troma movie Tromeo and Juliet made this word popular upon its release.