Warning: the following techniques may cause excessive eye-rolling and existential crisis in those who are not prepared.
Find a task that is marginally related to the actual task, but has an equally high likelihood of never being completed.
Example: If you're supposed to write a report, spend 3 hours researching a tangentially related Wikipedia article instead.
Link to: Advanced Procrastination
Tell yourself that your students are just not smart enough, or that you're just not good at teaching, or that the subject matter is inherently boring.
Link to: Justifying Your Incompetence
Use sarcasm to make your students question their own existence and the meaning of life.
Example: "Oh great, another exciting lesson on quadratic equations. Can't wait for the thrilling conclusion!"
Link to: Sarcasm as a Weapon
Remember, these techniques are not mutually exclusive, and can be combined in creative ways to achieve maximum fragility.