After playing some more, I figured out its easy to de-equip if your aiming but dont want to shoot. Just tap R
But I already found one nifty thing SK put in themselves.
*SPOILER ALERT*
The first "Book"
you pick up, if you drop it on the ground, its Alexia (i think thats her first name) Roivas.
*SPOILER END*
Pretty funny. Now I can't wait to see what else SK specially included in MGS.