'trigger happy' is always good for a laugh
This is a selection of clips, but the very first one cracks me up every time. Poor guy.
http://www.youtube.com/watch?v=nf8JtqAMZZk
(there's some swearing in this btw, so probably NSFW)
and here's another short one:
http://www.youtube.com/watch?v=2zgsi-cY4ww