Annoy popular celebrity crossing line (7)
I believe the answer is:
inflame
'annoy' is the definition.
(thesaurus)
'popular celebrity crossing line' is the wordplay.
'popular' becomes 'in' ('in' can mean trendy).
'celebrity' becomes 'fame' (celebrity can mean the quality of being famous).
'crossing' means one lot of letters goes inside another (to cross can mean to go over or around).
'line' becomes 'l' (used when specifying particular lines from a poem).
'fame' placed around 'l' is 'flame'.
'in'+'flame'='INFLAME'
(Other definitions for inflame that I've seen before include "Be provocative" , "Make (a situation) worse" , "Excite passionate feelings" , "Incite" , "Bother" .)