Setting the PIP_REQUIRE_VIRTUALENV environment variable
After several instances of accidentally installing packages into the global Python environment, I decided to look for a way to prevent this from happening. A quick Google search revealed that you can set the PIP_REQUIRE_VIRTUALENV environment variable to true to prevent pip from installing packages globally.
To ensure this runs every time I open a new terminal session, I added the following line to my .bashrc file:
# Prevent global package installation when using pip
export PIP_REQUIRE_VIRTUALENV=true
The only thing I'll need to remember is to set PIP_REQUIRE_VIRTUALENV=false when installing pipx to each version of Python I install with pyenv.