My personal example of that is from Italian (L2): it took me a few years to be able to reliably distinguish pairs like "pena" (pity) and "penna" (feather), simply because Portuguese (L1) doesn't care about consonant+vowel length.

I'd like to assume you changed the words of the mishap, and you we're actually in a restaurant, and instead of ordering "penne arrabbiata", you asked for an angry penis, "pene arrabbiata".

Like Tuukka there in a reply above this pointed out, the vowel length in the word "tapaan sinut" and "tapan sinut" in Finnish is very important, as the first one is "i will meet you" and the second one is "I will kill you". You can also change the consonants while having the same vowels if you just use the lemma of the word. "Tappaa" = to kill, "tapaa" = to meet

And a habit as in a custom, tradition, personal habit, would be "tapa", which is actually a synonym for "kill" in imperative form.

I like to imagine how fucking hard it would be to learn Finnish and thank my lucky stars I'll never have to.

Yup - we train ourselves to ignore distinctions as “not meaningful” because of our native languages, and then when we learn another language, one that uses those distinctions, it bites us back. You can get it later on, mind you, but it’s always a bit of a pain.

Yep, this is exactly what I've been doing through. I need to find an instance in English where a word uses the 싸 sound (ssa) but I still haven't found any yet!