Lorelai refers to the Haydens as “the Schnickelfritzes”. This is a variant of the slang snickelfritz, Pennsylvsania German slang given as an endearment to a child, most likely with the meaning “chatty kid, mischevious little imp”. Despite its affectionate use, Lorelai seems to refer to anyone she considers a massive pain in the rear as Schnickelfritz.
It may be a reference to Billy Wilder’s 1953 war film Stalag 17, set in German POW camp. To pass the time, the American airmen held in the camp bet on a “horse” race, where the horses are actually mice. One mouse named Schnickelfritz wins the race, even though the main characters were betting on another one. Lorelai may feel that the people she calls Schnickelfritz are similarly likely to ruin the fun and succeed where she’d prefer them to fail.
The film stars William Holden, who we later discover is one of Lorelai’s favourite actors, and on whom she has a celebrity crush. Holden won the Academy Award for Best Actor for his role as J.J. Sefton, and Stalag 17 was a commercial success, now recognised as one of the great war films of its era.