From Longman Dictionary of Contemporary Englishpuff something ↔ out phrasal verbpuff out your cheeks/chestHBH to make your cheeks or chest bigger by filling them with air Henry puffed out his chest proudly. → puff→ See Verb table
Examples from the Corpus
puff out• At the fence, he suddenly sucked his stomach in and puffed his chest out.• Cyril sat on the dock and took a long puff.• By the time she opens her eyes, ready, a half dozen little substitute puffs have blown out all the candles.• Exaggerated claims and puffs appear through out the text.puff out your cheeks/chest• Gillespie's cheeks puffed out as he blew into his bent-bell trumpet. 