Will it hurt the pi if I run a fan on the 3.3v gpio? I have a hdmi lcd screen on mine and I don't want to use the usb ports for a fan. I have a raspberry pi 3 by the way
The short answer is yes.
The long answer is yes, but...
3.3VDC is enough to run a low speed fan provided its designed for 3.3VDC.
I wouldn't try anything larger than a 40mm fan like this one, and this is why: the larger the fan blades are, the more torque is required to turn them, in in turn requires more power.
When you only have 3.3 volts, it takes 4 times the amount of current than with 12 volts most computer case fans run on. Also, the fan speed will not be as fast as the regular computer case fans either.
But yes, it can work for you.
A quick google search found a few pre-made options like this one on Amazon for one with a fan running on the Pi GPIO pins. .
I can neither speak for nor against either of these fans as I have not used them, they were just the first reasonable hits in my google search for "3.3v case fans".
You can draw up to 800 mA from the Pi 3.3V. See Raspberry Pi Power Limitations
Why you would want to run a fan (3.3V or other) on the Pi is a mystery.