The Telerik Bootstrap skin looks like it is Bootstrap, but it is not.  While it is easy to override a Bootstrap style to customize something, every time we do we end up on a support ticket to figure out how to make the same override in the skin.

One common area this comes up is the form sizing.  In Bootstrap, you can use a CSS class .form-group-sm to easily make the form controls smaller.  (There are several other classes as well for controls and form groups.)  The Telerik controls, like radCombobox or DatePicker do not honor this style, you need special Telerik CSS to get them to size.

The Bootstrap skin should have CSS included in it that handles when the Bootstrap control size classes are used.  That way when a Telerik control is placed in a div with .form-group-sm etc. it will automatically resize itself accordingly.

ref: http://getbootstrap.com/css/#forms-control-sizes