Sinfest has a surprising amount, considering it's nominally about one spikey-haired midget and his attempt to get laid, but notable ones are anytime Slick is honest about Monique, and many strips in the Uncle Sam series. Like this one.
The May 19, 2013 takes it another step for Lil' E. When his Mom, the Woman in White, is in hiding for "witchcraft and deviltry," he and her head to the Devil's mansion...only to be turned away by the guard on the Boss' orders (while said boss is partying with Baby Blue and a pre-Heel Face Turn Fushcia). The sad look the Woman gives her son as they leave, with Lil' E wondering about Daddy is heartbreaking.
Which makes what the Devil keeps in his high-security vault all the more painful. For a moment of pleasure with his two Devil Girls, the Devil turned away his son and his son's Mother.
He didn't hear them. He couldn't hear them. The damn music was so loud he never even noticed the intercom.