The One With Joey's New Brain - S7-E15
Character mistake: After Susan Sarandon slaps Joey the first time, after he tells her that her character is dying on DOOL, she turns away and right before she is off camera she smiles, instead of maintaining her anger. (00:06:05)
Origin of Iron Man: Part 1 - S1-E11
Character mistake: When young Tony Stark is telling his father that their helicopter's anti-flak chip didn't kick in, he acknowledges that it was his fault by saying he blew it. When his father corrects him and says "No Tony, we blew it. Stark and Son," Tony defensively says "The anti-flak chip failed, it's not my fault," completely contradicting what he said seconds earlier. (00:14:00)
Homeless for the Holidays - S3-E10
Character mistake: When Doug leaves work, he tells Carol he is Going Home to watch the channel 11 Yule log. Later on, he shows up at her house with Charlie and Carol says, "I thought you were watching the channel 9 Yule log." It's possibly a slip of the tongue from Carol, but most likely it would be ingrained in their heads which local channel features a Yule log at Christmas.
Behold, a Distant Star - S2-E10
Character mistake: When Sue is brought out of surgery, her father can be seen wearing a watch. Surgeons don't wear watches or any other kind of jewelry when performing surgery, as they can't be sterilized and can also get in the way of gloves. (00:05:00)
Character mistake: Geraldine's name changes from "Boudicca Geraldine Granger" to "Geraldine" but with multiple middle names from Mary Poppins with the surname "Granger."
Six Forgotten Warriors Chapter 4: The Six Fight Again - S5-E5
Character mistake: When the Red Skull reemerges from the vortex, he sees Chameleon and acknowledges him as his stepson. However, only moments before this, Kragov explicitly stated that the Chameleon was more like an adopted son to the Red Skull.
Kiss My Bum - S4-E10
Character mistake: Before Ellen invites Perry to thanksgiving there was only going to be seven for thanksgiving and yet whenever someone is asked about how many there are going to be at thanksgiving they answer eight.