Your plants or your freinds plants are like little baby humans. you wouldnt take your newborn into the sun with out first trying to protect them first. put your plants in a window whare ther isnt direct sun light for a couple of days. and gently move them into the direct sun light.
and I hope you freind didnt really put sun block on his plant. And if for some reason that he did. wash of the leaves with a spray bottle with luke warm water with a drop of mild dish soap. gently wipe the leaves off and rinse with luke warm water.