Will sticking plastic (PLA) in a usb port cause a short?
PLA will not cause a short, but some unusual formulations of PLA that include metal particles may be risky -- they are marketed as either &quot;conductive PLA&quot; or be designed with glossy, metallic finishes. For example, this PLA has a resistivity of 0.6 ohm-cm, which can easily lead to a short circuit in a USB port. It's also clearly marked as a conductive product. (as a side-note, these are also abrasive to extruders and will cause extruder wear unless you have one made with specialized materials/coatings)
From the perspective of electrical design, USB is already designed to tolerate pullups and pulldowns of around 15 kilo-ohms, as well as easily tolerating similar load resistances between VBUS and ground (which lead to current on the order of mA flowing). Meanwhile, PLA that doesn't include conductive filler is much more resistive by orders of magnitude.
There are further concerns with the brittleness; if you do print it, go for a solid infill to avoid the part snapping off inside the port, avoid weak points at any corners, and avoid mechanical loads with large moments. The full details of this involve slicer settings and are beyond the scope of this site.