It's rude not to return someone's text.
Bob just sent Jenna a text asking her on a date.
Jenna wants Bob to know she's not interested in him.
Jenna replies by text to Bob saying he's very sweet, but she's already dating someone.
Jenna pretends she never got Bob's text and doesn't text back.
Bob understands and respects Jenna as a person.
Bob feels very depressed and respects Jenna less as a person.