Remember when Max sings to Georg, "Compromise and be wise. […] You won't have to bow your head [to the Germans], just stoop a little"?
No? Oh, sorry—they cut that song from the film version.
Max Detweiler is a close friend of the von Trapp family; the kids call him "Uncle Max." He's a total opportunist, looking to make a buck or insinuate himself with important people whenever possible. He admits this completely. There's not much cynicism and irony in this film, but what is there comes from Max.
When it looks like Captain von Trapp and Baroness Schraeder are going to get hitched, Max very openly muses about how the match would benefit him, saying that he wants to make sure "all that lovely money" remains "in the family"— that is, in his vicinity, since he considers both Georg and the baroness like family.
Of course, the fact that Max doesn't even try to hide his selfish motives makes him a little more likeable—self-awareness can go along way. We see that when he's trying to get Georg to let the children sing in the Salzburg folk festival. Max pleads with Maria to convince her new husband to agree, saying first that not participating would reflect poorly on Austria… but then admitting that it wouldn't "do me any good either." He's always trying to angle for more status or money, but he's kind of loveably aware while he's doing it, which means he doesn't come off as a jerk.
As opposed to Georg, who's willing to sacrifice a lot in order to stand up to the Nazi regime, Max's attitude is that everyone should just try to get along with everyone and look out for oneself. He knows he doesn't have the captain's courage.
MAX: Things will happen. Make sure they don't happen to you.
CAPTAIN VON TRAPP: Max! Don't you ever say that again.
MAX: I have no political convictions. Can I help it if other people do?
When he can't persuade the captain, he goes to work on Maria:
MAX: Maria, he has got to at least pretend to work with these people. You must convince him.
MARIA: Max, I can't ask him to be less than he is.
Of course, Max does help the captain and his family get out of town, at great risk to himself—not to mention losing out on all the money he hoped to make promoting the Von Trapp Family Singers.
MAX: This strains my back and breaks my heart. . .when I think of the children missing the festival.
CAPTAIN VON TRAPP: By your announcement we'll be over the border.
MAX: Do you appreciate the sacrifice I'm making?
CAPTAIN VON TRAPP: You have no choice.
MAX: I know. That's why I'm making it.
Underneath Max's materialistic, cynical persona is a layer of compassion. When push comes to shove, Max comes through for the family he loves. He helps the von Trapps push their car to the road so the Germans won't hear them leave. When the family ends up having to sing after they're waylaid by Herr Zeller on their way out of the country, Max does a brilliant acting job after the performance, making it look like the escaping family is just backstage waiting for the awards ceremony.
But do we forgive him the occasional "Heil Hitler"?