Just wondering. Always heard it meant that.
You think anyone ever went out with a girl advertising “infectious smile” and woke up the next day wondering why his crotch itched and his date seemed grumpier than he expected?
No.
Infectious smile is simply a common figure of speech meaning that a person’s smile is so pleasing and genuine, that one can’t help smiling, too. IOW, one catch’s the ‘infection’ of smiling.
Although, wouldn’t it be fun if personal adds were full of such esoteric euphemisms?
“People applaud my good manners” = “I’ve got the clap.”
“Let me be the princess who turns a frog into a prince” = “Anal warts.”
“Good handy man around the house” = “wife beater.”
“Always in good spirits” = “alcoholic.”
Peace. (= “high”)