OK. I'll remember what you've told me and will be careful to avoid "rucksack" in my speech. To tell the truth I used to say it rather often when communicating and so far I've never noticed anyone mocking at me or giggling. Probably because those were people with good upbringing who weren't used to showing such kinds of reaction in public.
To be fair, I was probably exaggerating when I said that we'd be mocked, but I do feel that we 'rucksack'-users reveal that we are not as up-to-date as we thought we were.