How to hide select box drop down value - when one option is selected first time from the drop down?

[siva62]

Hi,

I have a requirement related to the Select Box variable in the Service Catalog Form.

1. When one option is selected from the drop down, next time the selected option should be hidden from the drop down.

Please find the below screen shot.

For example, if we can select the "system admin" first time, the next time "system admin" should be hidden.

2. The same requirement should be applied for all the drop down options in the select box.

3. Is there any script for this scenario?

   Please help me out for this requirement.

Thanks!