Heh. At my sister-in-law's 30th birthday party, I was feeling kind of awkward amidst the party people... so I decided on a whim that for her birthday? I was building her a blanket fort right there in the living room. (Plus, I could then hide in it.) Not only was she tickled by this, a couple of the guys joined in to help hang blankets where my short little self couldn't reach, and large portions of the rest of the party took place inside the fort. It was a great bonding experience.

tl;dr: Blanket forts are awesome, and not nearly so often inappropriate as one might think.