How to prevent tags from being deleted?

I'm using twitter typeaheadjs to populate labels on a page. I want to prevent the token from being deleted when the token value is equal to the login id.

I get the event from the docs :

Before the item delete event:

$('input').on('beforeItemRemove', function(event) {
    alert("before item removed");
    var tag = event.item;
    if(tag == DataMixin.data.user.username){
        console.log('cannot delete agent');
    }else{
        console.log('agent deleted');
    }
 });

Event after item removal:

$('input').on('itemRemoved', function (event) {
    alert("item removed");
        }
    }
});

How to prevent tag removal based on above condition in typeaheadJS