Mark Cuban Slams Y Combinator Co-Founder for Dissing Shark Tank in Ugly Twitter Feud Don't swim with sharks, not if you can't bite back.

Mark Cuban is a feisty one. He doesn't take kindly to people bashing Shark Tank.

Y Combinator co-founder and former president Paul Graham found out in a very public, ugly way yesterday. The billionaire (Cuban) and the millionaire (Graham) knocked horns on the little blue bird last night.

Graham fired the first shot, warning startups not to waste their time appearing on Shark Tank.

Startups: Instead of appearing on Shark Tank, spend that energy fixing whatever makes your product so unappealing you think you need to.

— Paul Graham (@paulg) January 28, 2016

Former Googler and Shark Tank guest star Chris Sacca, fought back first with a splash of sarcasm.

@paulg Yeah, because a free 10-minute pitch to 7 million Americans is something every startup should turn down.

— Chris Sacca (@sacca) January 28, 2016

Sacca's sneer didn't sit well with Graham, who's long written plenty about how hard founders like, for example, Google co-founder Larry Page, have it.

@sacca Nothing is less free for a startup than something that costs the attention of the founders.

— Paul Graham (@paulg) January 28, 2016

Next Graham fired off a link to a Wall Street Journal story featuring fellow Y Combinator co-founder Jessica Livingston's unorthodox advice to early-stage startups. Nutshell: Don't spend an iota of energy marketing an "initially mediocre product." Wait until it's perfect.

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@sacca Building the best product is how most startups win, not by marketing. https://t.co/Q2B8CjfCDc

— Paul Graham (@paulg) January 28, 2016

Sacca weighed in with another snarky two cents.

@paulg Agreed. Nothing is more distracting than traffic, users, installs, job applicants, and revenue.

— Chris Sacca (@sacca) January 28, 2016

Then Cuban stepped in the ring and the gloves really flew off. So what if he was a few hours late?

@paulg you mean like the sense of entitlement and arrogance they get when they become part of a YC class ? It's hard to wash it out

— Mark Cuban (@mcuban) January 28, 2016

Startups, accelerators and arrogance, naw, those never go together, especially not up in Mountain View, Calif., where Y Combinator is headquartered.

Cuban, known to be bit of a hothead at times, spit more fuel on the fire, implying that Y Combinator is a crusty has-been, that its heyday as a relevant accelerator is long gone. We're surprised the razor-tongued Pittsburgh native didn't use any of his usual salty language.

@paulg the real question is why does a startup become part of YC any more ? The good old days of YC are just that

— Mark Cuban (@mcuban) January 28, 2016

Ouch. Maybe Cuban's bite was enough to shut Graham up about Shark Tank, at least for now. Apparently immune to shark bait, he still hasn't yet responded to Cuban or Sacca. We're guessing he's saving his energy for one of his preachy trademark essays.