[Dog Gone]

You don't have to be smart to call yourself an environmentalist.

[SierraWasp]

You don't have to be anything at all!!! Any old Freakazoid with a big mouth will do!!!

[UCANSEE2]

You don't have to be smart to call yourself an environmentalist.

Maybe the defininition of the various parts would help?

Environ = place you live, abide, Earth, the dirt.

Mentalist= A specific order of, or having to do with the mind, or on the mind.

Put them together, and what do you get?

Dirt for brains.