A Marijuana adventure.
A weebo is the entire adventure including, but not limited to, the actual process of smoking. So when going hiking and smoking along the way, the entire hike is regarded as a weebo, not just the part when you were smoking.
There are no real requirements for the adventure as long as you and your friends consider it one. So a weebo could be anything from smoking in a new spot to a month long cross-country trip with a quarter pound.
"We went on a weebo at the state park today."
"We're looking for some good weed for our trip up north so we can make it a weebo."