I desperately needed a costume for my son's school Halloween party THAT SAME NIGHT, so I went ahead and put one together … with a few modifications for the lazy.
First of all, you can't buy spray paint in Chicago (and I didn't have time to wait for it to dry anyway) so I ran to Home Depot and bought a roll of the widest blue painter's masking tape they had (cost me about $11). Then I hopped across the street to Party City and bought a package of plastic bowls in the same blue ($4). I taped the box completely, then I cut the holes for my head and arms. (I use an old serrated steak knife to cut cardboard.)
After trying it on to gauge proper placement, I stapled the bowls to the front of the box with an ordinary Swingline stapler (not a red one). I used a stapler because I'm sure I have a glue gun around here somewhere, but bless me if I can find it. I asked my son to bring me a real Lego block for reference, grabbed a Sharpie, and wrote LEGO on all the bowls.
The whole costume, not counting driving to the store or the time it took me to move some bikes in the garage so I could get to the right-size box, was done in about twenty minutes. Sweet! No sewing required, even!
I have to say that it was really fun to be a giant Lego. Lots of kids came up to me and said "ARE YOU A … LEGO?" (I was good and said "Yes" and not "No, I'm a banana.") I also joked that Legos are very scary to parents. They multiply and always end up underfoot …
Thanks very much to Kate for the link and to Diana (and the folks at CRAFT) for the idea!