To be fair, he's talking this context in particular. I wouldn't be anywhere near as harsh, but would definitely frown on somebody replying to a legal contract w

To be fair, he's talking this context in particular. I wouldn't be anywhere near as harsh, but would definitely frown on somebody replying to a legal contract with a thumbs up to mean "I accept". If it were the other party, I would (and have) asked for clarification. Surprise; there have been multiple instances of potential disaster caught early this way!