The meme is humorous because it sets up an expectation of a moderate, controlled night of cannabis consumption with the phrase 'let's not get too high tonight', which is then comically contrasted with an image showing an absurd outcome of people dressed as traffic cones blocking a road, presumably because they got much higher than intended. The over-the-top result plays on the idea of unexpected and ridiculous situations that can occur when people are under the influence and don't stick to their initial plans.