There's a trophy dedicated to an especially hilarious easter egg.
Step 1: Play as Snake
Step 2: Go up to a locker and open it. If the poster is of a model in a bikini or something, Walk right in front of it and go first person view (Make sure to get a nice view of the poster as a whole).
Step 3: Call Otacon while in first person view.
Step 4: ???
Step 5: Profit