Q:

What is the difference between 敬仰 and 瞧得起

On the German/Chinese forum a guy was asking about how to say:
He is your little brother, that's why he looks up to you.
I wanted to use: 因为他是你弟弟，当然他瞧得起你。
I ask 2 Chinese friends, who both said no, '瞧得起‘ is unfriendly, use 敬仰。 However, they haven't given me an explanation I can follow about why '瞧得起’ is unfriendly, derogatory. I don't want to get on their nerves, so I'll ask here.
How does 瞧得起 deride someone? Do they mean: ‘You think he is great, but he is not.'?? 
How is 瞧得起/看得起 used?

A:

'敬仰' means 'respect and admire' ; 'look up to'.
If you say that you 敬仰 someone, you are humbling yourself.
'瞧得起‘  means 'consider worthy'
If you say you 瞧得起 someone, you are putting yourself in the position of judging that someone's worthiness (and in the position of granting favors to him or her) ;  you thanks someone for 瞧得起你 (consider you worthy) to show your humbleness.

因为他是你弟弟，当然他瞧得起你
... why '瞧得起’ is unfriendly, derogatory.

It is not unfriendly or derogatory, just improper in certain situations. It is perfectly acceptable to say: "your boss promotes you because he 瞧得起你". It is also fine to say: " A big movie star 瞧得起你 because he invited you to his party."
A younger brother is not in the position of judging his older brother's worthiness. Therefore, 瞧得起 is an improper term to be used in this instance.
Even for an older brother, it is still not right to say someone 瞧得起 his younger brother-- Brothers are expected to consider each others worthy by default.
Side notes:
敬仰 = 尊敬(respect)+ 仰慕(admire)
The opposite of 瞧得起 (consider worthy/ look favorably upon) is 瞧不起 (consider not worthy/ look down upon)

A:

敬仰是书面用语，适用于正式场合。瞧得起是口语，适用于街头巷尾。
另外，敬仰隐含仰视的意思，是自认身份较低的人对身份较高的人所说。
而瞧得起，则带有非常明显的俯视态度，有认为自己纡尊降贵的意思。
敬仰是书面用语，适用于正式场合。瞧得起是口语，适用于街头巷尾。
另外，敬仰隐含仰视的意思，是自认身份较低的人对身份较高的人所说。
而瞧得起，则带有非常明显的俯视态度，有认为自己纡尊降贵的意思。

One difference is that 敬仰 is mostly used in written, and in formal circumstances, whereas 瞧得起 is colloquial and more popular. 
Furthermore, 敬仰 implicitly conveys admiration,  it is used by someone - who puts themselves in a lower status - when referring to someone else of higher status. 
On the other hand, 瞧得起 carries an extremely evident sense of patronizing superiority and condescension.

