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

Company

Closing Price

CAPS Rating (5 max)

% Change

52-Week Range

Medis Technologies (NASDAQ:MDTL)

$2.72

*

(26.09%)

$2.69-$16.15

Circuit City (NYSE:CC)

$3.37

*

(21.26%)

$3.37-$15.99

US Airways (NYSE:LCC)

$2.54

*

(19.37%)

$2.39-$36.81

UAL (NASDAQ:UAUA)

$6.09

*

(14.94%)

$5.58-$51.60

General Motors (NYSE:GM)

$12.91

*

(6.38%)

$12.75-$43.20

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 isn't one of them.

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 when our 110,000-person-strong Motley Fool CAPS community of stock pickers speaks with a poor rating or a negative pitch. You should, too. Here's today's list of the worst stocks in the world.

Worse
We begin with Medis Technologies, which has a history of burning through cash and accelerating losses. Behold:

Metrics (mil.)

TTM*

2007

2006

2005

Revenue

$0.4

$0.4

$0.15

$0.425

Net income

($43.6)

($38.2)

($33.0)

($18.6)

Free cash flow

($70.5)

($72.5)

($39.6)

($21.4)

Source: Capital IQ, a division of Standard & Poor's.
*Trailing 12 months ended March 31, 2008.

Now, to feed the capital-crunching beast it has created, management plans to sell $29 million in stock and warrants. Shocking.

Medis has caught my attention before for diluting existing investors. Truly rule-breaking technology results in massive revenue growth -- and thus, equally massive profits. Where's the growth?

Worser
Next up is General Motors, which, according to The Wall Street Journal, will introduce margin-crushing incentives in order to prevent Toyota (NYSE:TM) from overtaking it as the top U.S. automaker.

Does it get any worse than that? Not when steel prices are rising like a rocket from Cape Canaveral.

Worst
But our winner, once again, is United Airlines parent UAL, which on Monday eliminated another 950 jobs. This time, pilots got the pink slips. (OK, furloughs. Call me when these pilots actually get to fly again.)

There's no way to sugarcoat this, so I won't. UAL is cutting jobs and capacity, which should lead to lower expenses as well as revenue. But with oil prices soaring, there's no guarantee the cuts will do much -- if anything -- to boost profits.

UAL and its maybe-this-time-we'll-cut-our-way-to-growth management team ... Monday'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.