He was chatting with a crew member in his makeup room and he reached out for the can of insecticide kept on his table without looking at the bottle and sprayed it on his underarms.
Only when his underarms had a burning sensation did he realize that he had used insecticide instead of deodorant.
He went on the sets, in spite of the pain and the stench. But the stench got stronger later and it was impossible to continue working like that. Ranbir then took a shower and continued shooting.
Ranbir is now going to be very careful about using deodorants now. As for the insecticide kept on his table, it was there because the production guys use it a lot to keep the flies away.