For me - spelling’s bad enough, but what about pronunciation? Hearing somebody mispronounce a word that we’ve all known since we were little chilluns makes me absolutely berserk. My particular favorites:
‘drownded’ instead of ‘drowned’
‘jag-wire’ instead of ‘jaguar’
and the crowning touch…
‘nook-you-ler’ instead of ‘nuclear’
Aargh.