Other mistake: Clarence tells George that his brother died at the age of 9 because he wasn't there to save him from falling through the ice, but when you see the tomb stone, it shows Harry Bailey was born in 1911 and died in 1919. That would make Harry only 7 or 8 years old.
Other mistake: During Harry's party, when George is outside talking to his mother she encourages him to see Mary and George says "Point me in the right direction." He then exits right and immediately returns. As he passes by, there is a glitch in the film and for a brief moment everything speeds up. This is most evident if you watch the people dancing in the house because they appear as though they clicked into "fast-forward motion" briefly and then return to normal.
Answer: It was a common phrase at the time, like someone saying "oh boy!" or "hot damn."