So, what are some really long surnames?
Googling about, I can find these last names:
MacGhilleseatheanaich
Ihakatommiehunnamorpukutemoi
Iturriberrigorrigoikoerrotakoetxea
But I can’t find a definitive list of long last names, including what the world record long last name might be.
In 1948, the Fijian cricket team had a fine player named Ilikena Bula.
Which was short for Ilikena Lasarusa Talebulamaineiilikenamainavaleniveivakabulaimainakulalakeba.
I’ll avoid quoting the Monty Python sketch. 
I did know a Barbara Featherstonhaugh.
Unlike RealityChuck, I make no pretense of restraint:
Johann Gambolputty de von Ausfern-schplenden-schlitter-crasscrenbon-fried-digger-dingle-dangle- dongle-dungle-burstein-von-knacker-thrasher-apple-banger-horowitz- ticolensic-grander-knotty-spelltinkle-grandlich-grumblemeyer- spelterwasser-kurstlich-himbleeisen-bahnwagen-gutenabend-bitte-ein- nurnburger-bratwustle-gernspurten-mitz-weimache-luber-hundsfut- gumberaber-shonedanker-kalbsfleisch-mittler-aucher von Hautkopft of Ulm
Walter Matthau’s name at birth was
Walter Matasschanskayasky.
You can’t get more long than my last name.
sorry, had to do it.
Oblong–
Well, then, what’s your last name?
Read it very slowly, Mr. Not.
Mr. ToKnow