"Liberals" who have nothing better to do than to join fashionable causes.
This term derives from liberals who sit around and drink overpriced diluted Starbucks coffee while lamenting the plight of the poor.
Latte Liberals have no sense of discretion and usually forget what they're arguing about soon after other latte liberals judge newer causes (polygamy, discrimination against left-handers, etc.) to be more worthy.
Note contrast to cornflake conservative
New Hampshire is invaded by Latte Liberals from Vermont once every four years.