An clitic requires a host. These words can stand alone: 

 un-fucking-believeable > fucking 

 Possessive 's is often considered a clitic in English. Note that it cannot stand on its own: 

 [that guy]'s hat > *'s 

 This, of course, is an enclitic, not an endoclitic. We have no real endoclitics in English (try looking at Tagalog). There is one historical left-over that is thought to have derived from an endoclitic, however. The /n/ in 'stand' is thought to be the present participle marker from Latin. Notice its absence in the past form 'stood'.