What is the cheapest way to damage myself and trigger the effects of the Fade Away feat?

For clarity, I mean cheap in the sense of the action economy. The ideal scenario would be to damage myself with a free object interaction or a small amount of movement.

Here is the relevant text of the Feat:

Immediately after you take damage, you can use a reaction to magically become invisible until the end of your next turn or until you attack, deal damage, or force someone to make a saving throw. Once you use this ability, you can’t do so again until you finish a short or long rest.