That seems like it starts to take on one of those weird lines of language-shifts-and-meanings-change ambiguity. (Like how very, very few people think of phrases like "whirling dervish" as being racist, because very, very few people know of any meaning to "dervish" other than "thing that whirls".)
My experience with derp is mostly from a particular gaming community (EVE Online), and it doesn't even vaguely match stuff towards the inability to speak of the mentally disabled, because something has to hit at least about 800 words before being categorised as "derping", and is generally to do with people chestbeating their own alliance or rationalising losing a battle. Of course, losing a battle could happen because you derped it, or because your tactical discussions were all herp derp, so then you accidentally the whole fleet. (The missing verb there was intentional. "Accidentally the whole [thing]" is an EVE thing too.)
I don't know, though - EVE has quite a few of its own jargon quirks, some of which have escaped into the gaming wild, but some of which haven't, and it's kind of its own special snowflake of language use.
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My experience with derp is mostly from a particular gaming community (EVE Online), and it doesn't even vaguely match stuff towards the inability to speak of the mentally disabled, because something has to hit at least about 800 words before being categorised as "derping", and is generally to do with people chestbeating their own alliance or rationalising losing a battle. Of course, losing a battle could happen because you derped it, or because your tactical discussions were all herp derp, so then you accidentally the whole fleet. (The missing verb there was intentional. "Accidentally the whole [thing]" is an EVE thing too.)
I don't know, though - EVE has quite a few of its own jargon quirks, some of which have escaped into the gaming wild, but some of which haven't, and it's kind of its own special snowflake of language use.