These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Woolseyism - When Kyon's little sister kicks Kyon upon his opening the front door in the first episode, she says death instead of desu (they're both pronounced "dess" in Japanese). This joke makes zero sense in English, so the subs give her the vaguely threatening "Nice to see you alive, Kyon!"
In the dub, she says "Welcome Back Attack" in which Kyon says that she changed a simple greeting into an attack. It works.