Laugh at the vehicle Giles is leaving on (6)
I believe the answer is:
giggle
'laugh' is the definition.
(I've seen this before)
'the vehicle giles is leaving on' is the wordplay.
'the vehicle' becomes 'gig' (gig is a kind of vehicle**).
'leaving' is a deletion indicator.
'on' says to put letters next to each other.
'giles' with 'is' taken out is 'gle'.
'gig'+'gle'='GIGGLE'
'at' is the link.
(Other definitions for giggle that I've seen before include "Laugh foolishly" , "Nervous or silly laughter" , "Laugh in a silly manner" , "Laugh nervously" , "Foolish or nervous laugh" .)