It’s no secret that Uber and Lyft don’t like each other much. In just one kerfuffle of late, Lyft told CNN that over a recent 10-month period, Uber employees had requested, then canceled, more than 5,000 rides from Lyft drivers. Uber quickly punched back, claiming that Lyft’s employees had canceled more than twice as many trips on Uber.

Investors in the rival ride-sharing services have mostly stayed above the fray through such public scuffles. But now, they’re starting to sling mud, too.

The trouble started yesterday morning, when at a TechCrunch conference in San Francisco, TechCrunch founder Michael Arrington interviewed Uber CEO Travis Kalanick in what appeared to be an effort to publicly rehabilitate Kalanick, who the press has begun to portray as something of a bully.

Arrington asked, for example, if it wasn’t true that Lyft is a copycat, partly because Uber and Lyft announced carpool options within a day of each other in early August. Kalanick, who typically seizes opportunities to trash competitors, humbly offered: “Here’s maybe a little bit of a hat tip: I don’t think Lyft copied this particular feature; companies are often working on similar things.” (According to New York magazine, Lyft began work on its program in April, but “before the Lyft news had landed,” Uber published a blog post announcing a “virtually identical service.”)

Arrington also uniformly dismissed Uber’s competitors as “ankle biters” and called Lyft “annoying because you have to sit in the front and talk, and they have those mustaches.” Said Arrington to Kalanick: “They seem to be constantly whining that [Uber is] beating them. Would you consider buying Lyft to shut them up?” (The audience laughed as Kalanick told him that Uber isn’t acquiring companies right now.)

Initially, the interview seemed a coup for Uber. Noting Kalanick’s gentler demeanor — Kalanick repeatedly called himself “scrappy” and misunderstood — TechCrunch reported that if “Uber can buck its perception as a ruthless, greedy company trying to put cabbies out of work and instead show the softer side of on-demand services, it could succeed far beyond taxis.” Meanwhile, the San Francisco Chronicle noted Kalanick’s “pains to exhibit his kinder, gentler side” during the on-stage interview.

But the cozy interview almost immediately drew criticism on Twitter, with comments from people like Wall Street Journal reporter Doug MacMillan and Founders Fund partner Geoff Lewis, both of whom noted that Arrington is an investor in Uber through his investment firm CrunchFund, an affiliation that was never raised during his interview with Kalanick. Lewis, whose firm has invested in Lyft, was particularly pointed in his tweets, calling Arrington’s interview “shameful,” given its absence of any relevant disclosures.

Things only grew more heated several hours later, when during an on-stage interview with TechCrunch’s Alexia Tsotsis, Peter Thiel of Founders Fund described Uber as “without question, the most ethically challenged company in Silicon Valley.”

(As Twitter lit up over Thiel’s remark, venture capitalist Marc Andreessen, whose firm also owns a stake in Lyft, joyfully jumped into the fray, tweeting: “A big thank you to @arrington for all the unsolicited free publicity for Lyft this morning at Disrupt!” He also published a discount code for Lyft — DISRUPT — and in Andreessen fashion, punctuated his tweet with a disarming smiley face.)

Arrington seemingly tried to stifle the conversation by tweeting to Lewis, “Let’s just cut to the ‘and the horse your rode in on’ and go our separate ways, you worthless d__k.” Perhaps realizing the tweet would only garner more attention, Arrington then tweeted that Thiel is an investor in Uber through Arrington’s fund, CrunchFund, and that Arrington is himself an investor in Lyft through Andreessen Horowitz, where he is a limited partner.

By then, though, Valleywag had caught the flavor of the story, calling out Arrington and Thiel for fighting over Uber “like boys with toys.” And Arrington’s efforts to help alter Kalanick’s public reputation as a brawler were largely forgotten.

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