Things I would have missed if my attempt in 2018 worked...
My attempts in 2019, 2020, and 2021!
The humor comes from the dark irony. The person is listing things they'd miss if their 2018 suicide attempt had succeeded. The punchline is that they would have missed subsequent suicide attempts. It's funny because it's unexpected and kinda morbid.
Dark
What about 2022?
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If the attempt in 2021 didn't work he would not have missed it