human lullaby
Someone so boring, so uninteresting, so powerfully dull that you find yourself suppressing the urge to yawn before they've even finished telling you their name.
"My date with Kelly from marketing? You mean, Kelly, the "human lullaby?" Let's put it this way--had I ordered the soup instead of the salad appetizer last night, there's a good chance I could have nodded off and drowned in my lobster bisque, she was so fucking boring."