For example:
Floccinauccinihilipilification
More:
http://writinghood.com/style/the-most-horrible-english-words/
Especially, how to read this nasty long word (it seems unrecognisable with its 1913 letters):
methionylglutaminylarginyltyrosylglutamylserylleucylphenylalanylalanyl-glutaminylleucyllysylglutamylarginyllysylglutamylglycylalanylphenylalanylvalyl-prolyphenylalanylvalythreonylleucylglycylaspartylprolylglycylisoleucyl-glutamylglutaminylserylleucyllysylisoleucylaspartylthreonylleucylisoleucyl-glutamylalanylglycylalanylasparthlalanylleucylglutamylleucylglycylisoleucylprolyl-phenylalanylserylaspartylprolylleucylalanylaspartylglycylprolylthreonylisoleucyl-glutaminylaspfraginylalanylthreonylleucylarfinylalanylphenylalanylalanylalanyl-glycylvalythreonylprolylalanylglutaminylcysteinylphenylalanylglutamylmethionylleu-cylalanylleuoylisoleucylarginylglutaminyllysyhistidylprolylthreonylisoleucylprolyli-soleucylglycylleucylmethionyltyrosylalanylasparaginylleucylvalylphenylalany-lasparaginyllysyglycylisoleucylaspartylglutamylphenylalanylthrosylalanyl-glutaminylcysteinylglutamyllysylvalylglycylvalylaspartylserylvalylleucylval-ylalnylaspartylvalylprolylvalylglutaminylglutamylserylalanylprolylphenylalanylarginyl-glutaminylalanylalanylleucylarginylhistidylasparaginyvalylalanylprolylisoleucyl-prolylisoleucylphenylalanylisoleucylphenylalanylisoleucylcysteinylprolylproly-laspartylalanylaspartylaspartylaspartylleucylleucylarginylglutaminylisoleucy-lalanylseryltyrosylglycylarginylglycyltyrosylthreonyltyrosylleucylleucylsery-larginylalanylglycylvalylthreonylglycylalanylglutamylasparainylarginylalanylalanylleucyl-prolylleucylasparaginylhistidylleucylvalylalanyllysylleucyllysylglutamyltyrosylasparaginy-lalanylalanylprolylprolylleucylglutaminylglgycylphenylalanylglycylisoleucylserylalanylproly-laspartylglutaminylvalyllysylalanylalanylisoleucylaspartylalanylglycylalanylalanylgly-cylalanylisoleucylserylglycylserylalanylisoleucylvalyllysylisoieucylisoleucylglutamyl-glutaminylhistidylasparaginylisoleucylglutamylprolylglutamyllysylmethionylleucylalaalanylleucyllysylvalylphenylalanylcalylglutaminylprolylmethionlysylalanylalanylthreony-larginylserine