The nasty, hardened leftover lotion on the opening of the bottle. Slightly crusty and yellow in color.
When found in normal lotion, one desperately tries to remove said crusty lotion with vigorous effort.
Bro! What did you just fling at my face?
Sorry, bro, I was putting on some lotion and found that nasty hard shit in it.
Ah, lotion crust, all is forgiven.