In the world of performance art, triple threats are those who can sing, dance, and act. They're a rare find, but well worth the price of admission to see a performance. In the world of prom dresses, triple threats are those dresses that are three times as ugly, with included pattern, poof, and too much bling. Though they are rare, they are not worth the money to buy this hot mess.
Example A:

Does anyone else find it weird that the boobs are sparkly, the hips have stripes, and the poof is plaid. I'm sure it does wonders for the figure.

Example B:

"Wow! Sparkly roses AND a waistband a mile wide. But wait, there's more! If you order within the next 10 minutes- 'cause we can't do this all day- we'll throw in a full, poofy skirt with gigundo roses and purple stripes for the low price of just $340. But wait! We'll even pay shipping and handling!"

(Gee, thanks. That's so generous of you!)

Example C:

"Holy Toledo, Pebbles! You and Bam-Bam are going to prom wearing matching suit and dress? That's so creative!"

"I know! He bought me this dress, and we're going to take Daddy's car for the night! Yabba-dabba-doooo!"