What do you call a friar when you see one in public ?

An open air friar?

Thank you folks, I will be here all week.

 A stupid idiot

A burger flipper!

"Brother". that is the correct way to address a friar.

You call him "Brother" if he has not been ordained a priest. You call him "Father" if he is ordained a priest. In any case, friars regard themselves as brothers whether they are priests or not. You can't tell by looking at a friar if he is a priest or not, so there is no offense if you mistakenly call a friar-priest a "brother."

Friar derives from Latin frater meaning brother  as in fraternity.

Say "Brother Smith," for example, if you're directly addressing the friar and Smith is his last name.