What: Shares of Gap (NYSE:GPS) were down 12.6% as of 12:15 p.m. Friday after the clothing and accessories retailer announced disappointing December sales results.

So what: Specifically, Gap revealed that net sales for the five-week period ended January 2, 2016, fell 4% year over year to $2.01 billion, hurt by a 5% decline in comparable-store sales during the month. That includes a 2% drop in comps at Gap, a 7% decline from Old Navy, and a steeper 9% drop from Banana Republic.

Analysts, on average, were expecting consolidated net sales to decline a narrower 3.5%.

Gap CFO Sabrina Simmons added, "As we bring the holiday season to a close, we look forward to delivering new Spring collections across our brands."

Now what: The latest slump caps a difficult year in which GAP stock declined a staggering 41% -- and in which clothing retailers as a whole struggled to to keep pace with consumers' shifting preferences. Worse yet, Old Navy was formerly a bright spot, with comps rising 4% in Gap's most recent quarter, but now the company's declines are proving more broad-based.

If course, this could simply underscore the challenge of difficult year-over-year comparisons and fierce competition in the crucial holiday period, which explains why Simmons prefers to look forward to the coming spring seasons. But for now, I can't blame Gap investors for hanging their shares back up on the rack.