Tell your friend who lost:
"You want to bark at, and then gamble with, a guy who you have no clue how he plays and then you want to blame someone else besides yourself? Give me a break. If you choose to gamble with people when you have no clue how well they play, then you are assuming the risk that he might be better than you and might win your money. If you don't like that risk, then don't gamble with people whose games you are not familiar with. You are a big boy who makes his own decisions and I didn't feel it appropriate to interfere."
or
"I figured if you were worried about losing you would have asked me how well he plays/who would be favored in the game. By barking at the guy and by not asking me my opinion it made it pretty clear to me that you were perfectly ok with taking the risk that he might be better and you might lose and I didn't feel it appropriate to question your decision and motivation. In the future if you don't want to lose because you didn't know someone's speed, you should probably find out what their speed is before barking at them and gambling with them."