Dear Married Sibling,
I received the text you sent that was meant for your husband. Thankfully it wasn't a naughty one, but I don't appreciate your obvious carelessness. I was fine when you made this mistake with Mother. I was fine when you kept doing it, and made it on another occasion with Father. But I will not tolerate you making that mistake with me. I will show you no mercy when I make fun of you at the end of this month. You can't avoid it because you already took time off from work and bought the flight tickets, plus you don't know what's coming to you. I promise you'll forever check your texts after I'm done with you.
Love your best, adorable, and only little sister