I can live with "glasses", "pants", "pliers" and "scissors", but "data" drives me crazy because even native speakers seem to be completely inconsistent when it comes to its number.
EDIT: Now that I think about it there is another one that is hard for me, even it I know it is the correct form in English: visa (singular) and visas (plural). In my mother tongue it follows the same pattern as datum and data, it's Visum (singular) and Visa (plural).
EDIT: Now that I think about it there is another one that is hard for me, even it I know it is the correct form in English: visa (singular) and visas (plural). In my mother tongue it follows the same pattern as datum and data, it's Visum (singular) and Visa (plural).