I am broke
No money at all

I can kick your butt
I am much superior than you

Idle rich
Person who are very rich and don't have to work.

If the shoes fit, just wear it
Learn to accept the reality

Ill at ease
Feel annoy

In a different league
Very superior

In a good light
Good qualification / personality

In a nutshell
In conclusion / in summary

In a word
Very short summary

In black and white
Formal (dress)

In like a lion, out like a lamb
Something that has a very good start but very bad ending

In one's cup
Drunk

In stitches             
Laugh out loud

In the light of
Have been considered

In the long run
In the long future

In the soup
In trouble

In touch
Keep contact

Inside out
From the inside to the ouside / Wear cloth on the wrong side

Into thin air
Gone without a trace

It beats me
Completely do not understand something

Ivory tower
A perfect, and unreal, place where everyone dreams to stay.