Never Touch an Instrument You’re Learning to Play
While Niles teaches Daphne and Roz how to play piano in Frasier S9 E7, his main requirement is to not touch the keys. They must first learn how using their practice pads.
When Phoebe attempts to teach Joey how to play guitar on Friends S5 E11, the same rule is true. Joey isn’t allowed to play a single string until he knows how and can pretend. She get very upset with him after discovering he is learning behind and playing behind her back.
Bank Errors
S10 E18 Martin kept receiving money that didn’t belong to him due to banking errors. It started off with $40 and he ended up with $10,040 after a security officer thought he was robbing a bank.
Phoebe also kept getting free money that wasn’t hers in S1 E3. Starting with $500 that was credited to her account, after first taking to the bank an additional $500 was added. She was annoyed just like Marten for having to deal with straightening all of it out.
Baby Blues
Monica and Chandler can’t have a baby because he has low motility and she has an inhospitable environment.
Niles and Daphne struggled to get pregnant. After going to the sperm bank and doctor, he finds out he has slow swimmers. It all worked out in the end because it turns out she has fast eggs.
Hacking Answering Machines
Both Frasier and Friends were not stopped by simple passwords and secret codes when it came to recorded messages. On Frasier S5 E8 Frasier is having a hard time understanding why a woman broke up with him. He asks all his family and friends what is wrong and unlovable about him. After admitting to everyone that he called her repeatedly for an answer about their relationship, he offered to play the messages he left for her on her machine. He knows the password because he helped her set it up.
The same kind of thing happened when Monica received a possibly new phone message from Richard on Friends S3 E2. After their relationship had ended and sometime had passed, she hears his voice in a message. She freaks out and asks everyone if it was new or not. They all decide it was old but Monica wants to find out for sure. So she calls and leaves an embarrassing message on his. She offers to play it for everyone and to their surprise she knows his passcode.
Same guy and nearly the same guy
Friends... Ross, meet Russ.
On Frasier, there was Niles and Rodney.
Ugly Naked Guy & Maris Crane
Throughout Frasier, Maris Crane is a driving character for many plots, yet she is never seen. The same is true on Friends with Ugly Naked Guy. Though he is only part of the first few seasons, he is often brought up yet never seen.