Here's how to make a wonderful(!) tie knob.
Visit this excellent site dedicated on this topic (french)

Step 1

The right part of the tie should be long enough to go as far as your knee, in fact it depends on you and the tie, try to find a mark.

Step 2

You must always turn around in the same way (here, I chose anti-clockwise).

Step 3

 

Step 4

 

Step 5

 

Step 6

 

Step 7

 

Step 8

 

Step 9

 

Here you are!

Nice uhh?

To get rid of it, simply hold the knob and pull the little end out.