Verb
(idiomatic) To smile, especially while attempting not to.
(idiomatic) To begin to smile.
Source: en.wiktionary.orgBorubaev, widowed, fond of a vodka, invariably caught between local and geopolitical forces, gangsters and the general toughness of Bishkek life, is so hardboiled he doesn’t crack a smile in any of the books. Source: Internet
Try not to crack a smile when listening to Novy run through his turn over DJ Name’s buzzy party-rap beat. Source: Internet
Darren McKay couldn’t help but crack a smile. Source: Internet
Perhaps most importantly, the humor failed for me; I didn't crack a smile once. Source: Internet