1. To press up to someone or something so firmly that it causes the person or object pressing to squish, contort, or deform. The package must have squashed up against something during delivery, because the box is all misshapen. I hate having people squash up against me on the train every morning when I commute to work.

2. To compact someone or something against someone or something else so firmly that it causes the former to squish, contort, or deform. A noun or pronoun can be used between "squash" and "up." The sudden rush of people squashed me right up against the window. Dang it—I squashed the bread up against the side of the shopping cart.