Why I generally hate fansubs.

It's most jarring when you hear a similar phrase translated so differently, going from "You punk" to "You shithead," just by your choice of sub group :lol

It's always weird seeing the team swear in Sentai. I'm use to it now, but the first time something serious like shit or fuck was said I did a spit take :lol

Perhaps worst of all, is if you watch a show enough to start to pick up certain phrases you start to realise which fan subbers are wrong or not.

Yup there's a difference between changing a foreign phrase to a culturally equivalent one because the direct translation sounds odd and just making characters swear because it "sounds cooler".

I've always seen it as sentai shows are for Japanese kids and Power Ranger are for American kids which if you think about it, is possibly more insulting than saying one is for adults and the other for babies. ;)

Even the classic Toku insult staple that is "ONORE" is more or less like hearing a stereo typical villain shout "Curses! Foiled Again!

Well, welcome to the traps of translating the Japanese language.

Saying one group is "wrong" isn't necissarily true. The Japanese language has very few ways to curse or swear somehow and based on intonation and situation, the gravity of the meaning can vary from "idiot" to "asshole". But basically, it's also a matter of personal interpretation, so in the end, it always depends on what you think the person meant.
It's easy to insult people in Japanese anyway, after all, there's even impolite forms of saying "you".

Not an insult, but rather a lie :P