If you are a buyer that lives in 99.9999% of the world: every. single. one. of. your. purchases. is. in. fiat. 

That is the unit of account you must adhere to in order to complete the purchase. You must convert whatever other stores of value you use into the unit of account if you'd like to complete a transaction. If you'd like to eat, you better adhere to the local unit of account.

This is not difficult? 

CliffBadger

bitcoin

Saying 1 btc = 1 btc when fiat price goes down is stupidity/cope

79c9095526

Its not only the vendor's standard unit of account. You (the buyer) also has to adhere to that standard unit of account by converting whatever asset you want into the standard unit of account in order to complete the transaction. 

Every bitcoiner (except a couple in el zonte or bitcoin jungle?) conforms to the fiat currency standard of account for their geography when they want to make a purchase.