Problem with ListBox in ASP.NET

Question

Hi,
Top of the hour to you all. I have got this little problem in asp.net c#. I have got a ListBox which some listItem like

Mango
Orange
Banana

I want to achieve this, when a user clicks on a list item for example click on 'Mango' the mango ListItem should only be disabled in the ListBox ....

Thanks in advance