The image shows a humorous exchange in the form of a meme between a patient and a dentist. The patient appears to be a middle-aged man, sitting in a dental chair, with a somewhat puzzled or pained expression on his face as he touches his cheek where the problematic tooth might be. The dentist, a woman in dental scrubs with a mask hanging around her chin, stands beside him, her body turned toward the patient, as if she is attentively listening to his complaint.
The top part of the image features a caption that sets up the scenario: "Me: My tooth hurts when I suck". This statement by the narrator (presumably the individual in the dental chair) indicates that they are experiencing dental pain during the action of sucking.
The caption continues with the dentist's supposed witty reply: "Dentist: So you're in constant pain". This punchline plays on the double meaning of the word "suck" — one referring to the physical action that might cause pain due to a sensitive tooth and the other implying a more colloquial use of the word to describe someone's general state of being or performance.
The humor in the image arises from the unexpected retort by the dentist, which takes a simple dental complaint and turns it into a playful insult about the patient's overall efficacy or success, suggesting they are metaphorically 'not good' at things on a constant basis.
Why people might find this funny relates to the element of surprise and twist in meaning. At first Me My tooth hurts when I suck Dentist So you re in constant pain