The One With Chandler In A Box (Season 4, Episode 8)

The Plot: Monica is reminded of a prior romance, and Chandler goes to great lengths to mend his connection with Joey.

As the gang judges Monica for her romantic interest in her (much older) ex-kid boyfriend's (which leads to a superb dissection of everyone else's romantic and life failures by Monica), Thanksgiving becomes unpleasant. Meanwhile, Chandler places himself in a cage to atone for kissing Joey's ex-girlfriend, Kathy. The extended play with Chandler in the box is plenty of laughter, but the emotional high point of the episode sees Kathy (Paget Brewster) realizing she couldn't break up Joey and Chandler's friendship, forcing Joey to go past his rage and rescue Chandler from the box so he may pursue the lady he loves. It's a good reminder of the characters' strong fondness for one another, as well as the dimension it provides to the program.

Link: https://www.imdb.com/title/tt0583515