Bad days. We all have them; some of us deserve them. Here are five stocks whose naughty ways drew investors' scorn on Tuesday:

Company

Closing Price

CAPS Rating (5 Max)

% Change

52-Week Range

UAL (Nasdaq: UAUA)

$13.55

*

(36.77%)

$12.78-$51.60

Omnicell (Nasdaq: OMCL)

$11.91

**

(29.82%)

$11.00-$31.12

AirTran Holdings (NYSE: AAI)

$3.61

**

(20.83%)

$3.26-$12.65

Meredith (NYSE: MDP)

$32.19

***

(13.79%)

$32.03-$63.41

Carlisle (NYSE: CSL)

$30.50

*****

(9.79%)

$29.01-$51.57

Sources: The Wall Street Journal, Yahoo! Finance, Motley Fool CAPS.

Naughty?
Well, OK, we can't exactly call these stocks naughty. There are days when five-star winners and newsletter recommendations appear here. Today is one of those days.

But, if you're an investor, you'll have plenty of bad days. The trick is to avoid dating -- or, worse, marrying -- your losers. That's why I listen -- and why you should, too -- when our 97,000-person-strong Motley Fool CAPS community of stock pickers speaks with a poor rating or a negative pitch.

Thus, here is today's list of the worst stocks in the world.

Worse
We begin with medical-device maker Omnicell, which yesterday reduced its estimates for 2008 revenue and profit.

Actually, that doesn't quite capture it. Omnicell took a hatchet to estimates. The company now expects to earn between $0.65 and $0.75 a share, down from $0.85 to $0.88. Revenue, meanwhile, is expected to grow from 17% to 20% year over year. Executives originally projected 25% to 28% top-line growth.  

CAPS investors probably aren't too surprised, thanks to the writings of All-Star CrankyTexan. Quoting from our Fool's October pitch:

I am a registered nurse who has used Omnicell machines. I hate them. [T]hey slow down my job. When I am rushing to get an item during surgery, the last thing I want to do is swipe my I.D. card, swipe the patient's information, and press a button when I take an item. A hospital using Omnicell is a hospital at which I do not want to work. [Emphasis added.]

Rarely is it a good sign when the front-line personnel who are supposed to benefit from a product "hate" using it.

Worser
Next up is AirTran Holdings, which, like peers Southwest (NYSE: LUV) and JetBlue, suffered from higher fuel prices in its first quarter.

AirTran said that fuel costs rose more than $100 million, enough to transform last year's $0.02-per-share gain into a $0.38-per-diluted-share loss.

Worse, AirTran on Tuesday issued $65 million in convertible notes and 14.3 million shares of common stock. Exactly none of the proceeds will be used to fund growth. Or at least not until 2009, at the earliest.

Instead, Kevin Healy, AirTran's senior vice president of marketing and planning, told Forbes in an interview that growth will remain in a "holding pattern" until the carrier can ensure that it has the funds to operate independently.

Worst
But our winner is United Airlines parent UAL, which makes the list for all of the reasons my Foolish colleague Brian Pacampara referenced, and one more: labor.

Whether you love or loathe unions, the undeniable truth is that they have a substantial say in how business gets done in the airline industry. Yesterday, after executives said that additional layoffs and cost cuts were forthcoming, a spokesperson for the Teamsters, which represents UAL's mechanics, said the union would be "unlikely to support any proposed merger in an atmosphere of layoffs."

Translation: We don't care if you want to merge with Continental. Take our jobs, and we'll take your merger.

Anyone else think that a combined Delta (NYSE: DAL) and Northwest looks pretty good right about now?

UAL and its lousy labor relations ... Tuesday's worst stock in the CAPS world.

Do you agree? Disagree? Let us know what you think by signing up for CAPS today. It's 100% free to participate.

I'll be back tomorrow with more stock horror stories.