"Unintentional laughter" refers to laughing without intending or trying to be funny. It happens when something unexpectedly makes you find amusement or joy, even though it wasn't meant to be funny. Full definition
Everyone in the theater broke out in unintentional laughter when they made their appearance. (theartsdesk.com)
An interminable series of indistinguishable chases, explosions, catty one - liners, and PG - 13 leerings at T - shirt clad bimbos, Driven is a singularly cruel endeavour in that it inspires unintentional laughter in which we can not indulge for the beginnings of a crippling headache. (filmfreakcentral.net)
Where Hosseini was very poetic in describing Amir and Hassan flying their kites, Forster opts for a heavy handed, sentimental approach, which will either cause unintentional laughter or annoyed «alright, we get it» groans. (rottentomatoes.com)