S08E11 The One with Ross's Step Forward
Ross and Mona took pictures of themselves at the Rockefeller Center and now Mona wants to send the picture as a Holiday card to friends. Ross freaks out at the thought of them sending out Holiday cards together because they've only been dating a couple of months. Ross tries to have a conversation about their relationship and says all the wrong things and ends up giving Mona a key to his apartment. Chandler has to tell his boss that he split up with Monica in order to prevent that Monica has to have dinner with Chandler and his boss.