I have a 2011 VW Jetta Clean Diesel TDI. I love the car, but I
really dislike the key that comes with it. The key is a "switchblade"
design where you press the button (in the lower right of the picture)
and the key swings out.
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The problem with this is that the button protrudes from the rest of
the key and any little bump opens the key - even when it's in my
pocket. It's been annoying me for a couple of years.
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This fix is actually pretty simple. I made a little guard that you glue
around the button with superglue. It prevents the key from being
accidentally opened.
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I've included the skp file in case anyone needs to modify this for a
different key. See instructions for how to install it.

I made this with black PLA to match the key.
100% infill, .2mm layers, no support.
I was able to print it without a brim, but some printers may need
one to get it to stick to the build plate.
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To install,
*Put a little super glue on the flat side
*Line up this thing around the button with the flat (glue on it) side
toward the key, and the taller half toward the back end of the key
*Then press in place (you may want to dry fit it first before gluing)
*Be careful that you don't glue the button to the guard!
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To open the key, press the button as usual; the guard is angled to
allow your finger to fully press the button in.