Stupidity is contagious -- even respectable companies can catch it. As we do every week, let's take a look at five dumb financial events this week that may make your head spin.

1. Coach isn't first class
Coach (NYSE:TPR) continues to lose its grip on the country's luxury handbag market. Coach shares slipped on Wednesday after posting disappointing quarterly results.

The maker of once-trendy purses and fashionable accessories has been falling out of favor, which was evident in its latest quarter with sales sliding 6% on a brutal 13.6% decline in comps at its North American stores.

Analysts see revenue growth resuming when its new fiscal year begins in July, but winning consumers back to a brand in a state of decline is a difficult feat to pull off.

2. From hero to zero
Hercules Offshore
(UNKNOWN:HERO.DL) ran into some rough waters after a disappointing fleet status report out of the shallow-water driller. Even though revenue per day per lift boat and utilization rate show sequential and year-over-year improvement, it wasn't enough to please the market, sending the shares 15% lower on Thursday.

Analysts were not impressed either. Capital One and Global Hunter Securities downgraded Hercules Offshore on the news. Capital One lowered its price target on the shares from $11 to $8.

3. BlackBerry's last line of offense
 (NYSE:BB) was moving higher after a Department of Defense press release led some to believe that an order for 80,000 new BlackBerry smartphones had been placed, but sadly that wasn't the case. 

The Department of Defense's announcement about the launch of a new mobile network supporting 80,000 BlackBerry devices was for older BlackBerry phones that were already in its possession. The agency clarified that position to The Verge, turning what seemed to be an initial victory into yet another categorization of BlackBerry phones as old technology. 

4. Chips ahoy
Advanced Micro Devices (NASDAQ:AMD) slumped after following up strong results with a weak forecast for the current quarter. The holiday quarter was solid with a 38% surge in revenue. That wasn't a surprise, with AMD fueling the Xbox One and PS3 that were introduced in November. Margins weren't as inspiring. 

However, it's AMD's outlook calling for a larger than expected sequential decline in revenue -- on challenging gross margins -- that ultimately weighed on the otherwise resurgent chip maker.

5. "Polar vortex" isn't a new McFlurry
McDonald's (NYSE:MCD) keeps struggling. The world's largest restaurant chain posted another problematic quarter. Comps fell for the period, and that includes a 1.4% decline in domestic comparable-restaurant sales.

The restaurant-level performance worsened in December, and while it's easy to blame the wintry weather there are still plenty of restaurant operators checking in with positive comps during the holiday quarter.

McDonald's was hoping that limited-time promotions and the introduction of an expanded Dollar Menu & More slate would win back diners, but it's been more grimace than Grimace at Mickey D's these days.