I won't write a lot of words in here...
Environment: SP Online, Publishing Portal
Problem: jQuery.off(), jQuery.unbind(), element.removeEventHandler didn't work so we need to find a way to remove event handlers.

SharePoint uses Sys.UI.DomEvent.addHandler (alias $addHandler) and Sys.UI.DomEvent.addHandlers (alias $addHandlers) to add DOM events handlers.
If you want to delete absolutely all handler for all events everything is simple - just call Sys.UI.DomEvent.clearHandlers and put your DOM element as a parameter.
But what if you want to delete handlers of particular event?..
In that case you can use Sys.UI.DomEvent.removeHandler (alias $removeHandler) to remove added handlers... But the thing is that you need to know the handlers' functions to use this method.
After some investigation I've found that added handlers are stored in _events attribute in DOM element:

The functions that we need to use $removeHandler are stored in handler property of each item in the array of particular event handlers.
And here is an example of code to use to remove all 'click' handlers from 'form' element:

var $form = jQuery('form');

if ($form.length) {
  var formEvents = $form[0]._events;

  if (formEvents && formEvents.click) {
    jQuery.each(formEvents.click, function (clickIndex, clickHandler) {
      if (clickHandler.handler)
        $removeHandler($form[0], 'click', clickHandler.handler);

Have Fun!