Unpucker

unpucker your lips

Source: wiktionary

King. "Bethink you a little; I will walk about" (Gellert bethinks him, brow puckered. King , seeing the brow unpucker itself.) "Well, have you one?"

Source: wiktionary

How I wish I could whistle! If I could pucker up my mouth, and pitch it to just the right key, I wouldn't unpucker it in a week.

Source: wiktionary

Now, deep inside the Desert Camouflage Uniform pants of the most nervous staff officers crowded around SMOG stations in the palace, assholes were starting to unpucker — if not quite all the way, then there was certainly a little more sphincter breathability in the wedged-up cotton Hanes; or, in the case of those who went commando, the sandy folds of DCU'ed butts.

Source: wiktionary