Dear Beluga,
In this conversation, the term 'plus' serves to highlight a play on the word "blow." The exchange revolves around one character asking why another's eyes are watery and bloodshot, to which the response includes a suggestion to 'blow' them to alleviate the condition. However, the second character interprets "blow" in a different context, likely with a sexual connotation, leading to the humorous misunderstanding. The use of "plus" at the end indicates an additional layer to the joke.
I wish this explanation clarifies. Please feel free to reach out if you haven't understood the joke yet and pardon me being vague to stay within appropriate boundaries :))