So, this is what it looks like when Heidi Montag is “acting.”

Hubby Spencer joined The Hills starlet and her recently-inflated bosom on the set of Montag’s first movie on Monday. The blonde has been cast in a cameo role in the romantic comedy Just Go With It, which stars Jennifer Aniston, Adam Sandler, Brooklyn Decker, and Nicole Kidman.

The feature opens Valentine’s Day 2011….