Learn English – What adjective do you use to describe a curve that’s very curved?”

I feel like I'm missing something, but easily replaceable or just replaceable seems like the obvious answer. Certainly, people are frequently referred to as irreplaceable when they're not easily replaced.

The two examples you give seem to me quite different. In the first case, you're saying that you've done them a favor and they owe you, and yet you politely word requests in a deferential manner. The famous actor example seems quite different, like they have to give him what he wants because he's rich and famous and powerful, not because he has done anything for them personally.

"Oily" and "smarmy" are definitely NOT appropriate terms for the first case. Both have very negative connotations. These words are normally used to describe a salesman or a politician who pretends to really care about the other person but is in fact being completely selfish and usually deceitful.

Perhaps words that would fit here are "unassuming" or "unpretentious". These mean to not take advantage of one's position or to insist on the respect or deference that one is arguably entitled to.

The case of the actor seems entirely the opposite: he is demanding excessive respect for his social status. I'd call that "pretentious" or "presumptuous".