Can I pay with Paypal?
Yep, you can!
Once you've selected all the items you'd like to purchase, you can checkout through Threadless' regular checkout process. When you get to the 'Payment Info' section of checkout, select PayPal as your payment method. You will be taken to PayPal's site to set up your payment. Once you complete payment, just sit back and wait for your Threadless order email confirmation.
If you have an Paypal existing account, go ahead and use it, or create a new one while you're checking out.