There are some stocks that seem to be in everyone's portfolio, like big blue chips that most everyone can agree provide a reasonable measure of safety and appreciation. The "slow and steady wins the race" mantra almost necessitates their inclusion.

But there are also certain stocks that shouldn't be included in your holdings. There are some companies plagued with flaws significant enough that I'd never touch them. You'll never find Blue Apron (NYSE:APRN), Snap Inc. (NYSE:SNAP), or Shake Shack (NYSE:SHAK) in my portfolio. And I'll tell you why.

Blue Apron meal kit

Image source: Blue Apron.

Blue Apron

The leading meal-kit delivery service, which went public with so much promise, has been a major disappointment to investors. Although a lot of similar services already compete against Blue Apron, it wasn't until Amazon bought Whole Foods Market that its lack of a competitive moat was exposed for all to see. It only took the potential for a single, well-financed player to enter the market for the wall of confidence around Blue Apron's business model to come tumbling down.

There were also a lot of cracks in the company's foundation. Revenue growth is on a perpetual slide, customer acquisition costs are rising, it's losing customers as it cuts back on marketing, average order values are falling, orders per customer are down, and average revenue per customer is off as well.

Shares of Blue Apron have lost half their value since the June IPO, and I see little chance they'll be rising much anytime soon. completed its Whole Foods acquisition and immediately dropped prices for a slew of items in the upscale grocery store. It also recently soft-launched a Seattle-only test of its own meal-kit delivery service that -- thanks to the company's massive built-in population of Prime subscribers -- could quickly gain market share if it chooses to take the offering national. Blue Apron's stock may look depressed at the moment, but its share price today may soon look optimistic compared to where it ultimately ends up. Count me out.

Group of friends on their smartphones

Image source: Getty Images.

Snap Inc.

Like Blue Apron, social media platform Snap was one of the most highly anticipated IPOs of 2017, but the reality of the offering was simply too much for the market to bear. Although its stock has rebounded a bit in recent weeks, shares of the vanishing-message service have lost about half of their value since hitting the market.

Wall Street's concerns about Snap are similar to their misgivings regarding the meal-kit delivery service: Its growth is slowing dramatically, competitive pressures are rising, and management presents a muddled view of what the company's future should be.

Yet analysts remain a bit more hopeful about Snap than about Blue Apron. They liked reports suggesting Snapchat may have an edge over Facebook (NASDAQ:FB) on the " stickiness" front when it comes to teens, and some industry watchers are looking forward to the prospect of it developing original content. But you still won't catch me owning Snap shares.

Snap will need to boost its stickiness level up to "super glue" if it's going to turn around daily active user numbers and find a strategy to confront the challenges Facebook's Instagram poses.

Moreover, because Snap's dual-class structure gives outside investors no voting rights -- and thus no say in how the company is run -- shareholders will have to fully trust that management can implement its plan flawlessly. I wouldn't have the confidence and I won't be buying shares.

Shake Shack cheeseburger

Image source: Shake Shack.

Shake Shack

Of the three companies on this list, the better-burger shop is the one stock most likely to eventually change my mind. While it faces a plethora of challenges, it is the one least likely to be ruined by them. But don't expect me to backtrack on my position about it anytime soon.

There are clear indications the "better-burger" fad has run its course: High-end burger shops from Shake Shop to The Habit have seen comparable-store sales growth grind to a halt or begin to fall. Last quarter, Shake Shack said "same-Shack sales" (its variation on comps) dropped by 1.8%, the second straight quarter they declined. Worse, store traffic looks like it is beginning to fall off a cliff.

On an annual basis, Shake Shack traffic was up 5.5% in 2015, just 1.1% higher last year, and is now negative over the first six months of 2017.

The problem is that too many other better-burger shops have opened, and despite slowing sales growth, all the major chains in the niche are maintaining aggressive growth policies. Even Shake Shack, which may be the most conservative of the bunch, still plans to open dozens of new restaurants. With so many similar options in front of the relatively limited number of people willing to regularly pay for high-priced hamburgers, there's a market ceiling above Shake Shack -- and it may already be hitting it.