The Toyota Prius will go down in history as a truly ground-breaking vehicle, both the first and the highest-production hybrid vehicle built to date.

It's also the sole vehicle sold in the U.S. this year that is rated at 50 miles per gallon combined--for three different models, no less.

But a new analysis suggests that the perception of the Prius brand may be changing, and rapidly at that.

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According to an analysis of social media conversations by Networked Insights, a marketing analytics firm, the "brand health" of the Prius in social media has declined by 50 percent over the last 12 months.

The study looked at social-media discussions of hybrid cars, in which the Prius was mentioned in only 17 percent (a surprisingly low proportion, given the huge presence of the Prius family in U.S. hybrid sales).

Sample of negative brand perceptions of Toyota Prius on social media [slide: Networked Insights]

But more than one in seven of those conversations mentioning the Prius was negative, a higher proportion than in past years.

The analysis suggested that the Prius "no longer represents an eco-friendly alternative, but a humorous, weak, and sometimes un-American brand."

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Disturbingly, almost one in four Prius conversations (23 percent) included a slur or offensive comment--and 16 percent referred to the Prius as weak and unreliable.

While weak performance may be accurate in terms of acceleration, the fuel efficiency of the Prius is certainly anything but weak.

Sample of negative brand perceptions of Toyota Prius on social media [slide: Networked Insights]

Still, Networked Insights notes, "The negative comments range from mildly derisive to venomous--the brand has been hijacked as an adjective for everything considered stereotypical with the political far left."

Some of the analysis is quite funny: "Many negative comments about Prius were associated with NPR listening, Obama-loving, un-American liberals and the hashtag #Merica."

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Apparently Prius drivers also drink unsweetened tea--an activity seemingly viewed in a negative light, which left us scratching our heads. Then there's the puppy-kicking.

The tenor of some of the comments, frankly, reminded us of nothing so much as the adolescent but annoying practice of "rolling coal."

Pickup truck

The report ends by suggesting that Toyota needs to embark on a more aggressive effort to counter the "hijacking" of the Prius brand by such assertions.

The third-generation Toyota Prius is now in its sixth year and approaching the end of its model life, with an all-new 55-mpg Prius expected to be unveiled this fall.

CHECK OUT: All-New 2016 Toyota Prius: What We Know So Far

And gasoline prices in the U.S. are now lower than they've been for much of that car's life.

These two factors have led to a natural decline in Prius sales across the model range.

2015 Toyota Prius C

But while they still represent a minority of Prius perceptions on social media, the tenor of such comments and their growing prevalence clearly represent a threat to the long-term brand health of Toyota's proudest and most advanced vehicle.

And with the advanced-tech mantle having shifted from hybrid-electric vehicles to plug-in electric cars--which Toyota consistently impugns--the next Prius will no longer be able to claim technology leadership for the Prius.

Which leads to an interesting marketing conundrum: What if you launched at an all-new 55-mpg vehicle for 2016, and negative reaction made up a significant portion of the total?

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