If you have two items in your inventory, select the item that you don't want to disappear, then very quickly (as in pretty much instantly) press the number of the item in the hotbar that you want to disappear, as well as Q (or the drop item button).

For example:

I have steak and a sword in my inventory.

The steak is in slot 2, and the sword in 1.

if I hover over 2, and press 1 and q at the same time, the steak will be thrown, and the sword will disappear out of the inventory, until it is clicked in the inventory screen, or thrown as well.