If a coach is questioning on me about a call, or lack there of by my partner - one of my favorite responses is 'Coach - if I can give you an answer to that, you should be yelling/b*tching at me for not watching the players in my primary/the 6 players directly in front of me.' (you can either condense or elaborate depending on the time you have to talk to the coach and/or your repoire with the coach) The coach usually has to stop for a second to think about what you just said and it adds a little humor to help diffuse a situation.
This of course doesn't work if your partner has reached a little out of his/her area and called something you chose to pass on. Then it is a standard 'Coach, I am sure *insert name here* will happily explain it next time he/she has a moment.' Or you can just throw them under the bus with 'Hell if I know Coach, as soon as you figure out let me know'