Because they have a hard time puckering their lips the right way.
Causal fridays.
If they are thick, they have a hard time to rise
HIM: "A bear attack." ME: "Never heard of him."
The silence of the lambs
She only puckers up for her pacifier.
When a woman can easily move her lips after she applies it
Tulips
Because dogs can't whistle. (X-post from r/dadjokes)