The title of your post gives a big hint. If they perceive campaigners as weirdos (and most of the public do) then you need to:
1. Act utterly normal.
2. Make campaigning seem utterly normal.
A couple of suggestions:
a) Go to a local NO2ID meeting. Befriend anyone who would fit in with your friends. Invite them out for a drink with your friends.
b) Invite all your friends round. Persuade them they want to watch a DVD and then tell them you've got Gattaca out. Children of Men or Brazil are also good but the campaigners get seriously persecuted.