Beattie vs Chelsea in Feb 2005 - sent off for headbutting Makelele(?) and we had nothing to threaten Chelsea with for about three quarters of the game. It actually scares me that for nearly 2 years he was our sole striker!
Weir and Hibbert vs West Ham in Dec 2005 - Hibbert didn't do a damn thing right as far as I remember and Weir scored a dreadful oggie while sporting the biggest bonk-on in history.... ever.
Kroldup vs Villa in Dec 2005 - Spoilt for choice with this one ending 4-0 to the melts, but dear god....
Neville vs Wigan in March 2013 - Horrible horrible man, a bottler of the highest order and was the personification of Moyes' negative traits.
Barry and Alcaraz vs Hull in January 2015 - I still have nightmares about the game. The performances above this were GOD compared to that debacle! Loudest cheer of the day when Alcaraz got red.
Also, dishonourable mentions to: Nyarko vs Arsenal (April 2001), Unsworth vs Arsenal (March 1997), Materazzi vs Sheff Wed (April 1999)
For worst opposition players I'd go for:
Pepe Reina (RS 2006 - showed great reflexes in catching Johnson's head...)
Paul McShane (Sunderland 2007 - already mentioned)
Gary Kelly (Leeds 2003 - McFadden literally raped him)
Mickael Forsell (Birmingham 2006 - We had diddly squat to play for but Brum needed a win to survive, we weren't great but they were rank! Couldn't threaten us at all even with a proven gooser up front! Ended 0-0)
Gary Doherty (Spurs 2004, Norwich 2005 - terrible in both games!)
Bjorn Tore Kvarme (RS 1997 - pwned by the squid!)
Could go on