Just saw this, and not sure if OP's explanation was enough to make it click for you. The tattoo basically reads: "life is the sum of the daily struggles from birth to death", which is pretty bleak. But the shitpost comes in when you actually evaluate the integral.

This becomes sruleg^2 * (t^2 / 2) evaluated at death and birth, so:

Which simplifies to:

And the last bit of the shitpost is that they evaluated the letter "i" in birth as i, so i^2 = -1. And then you get the result in the image, minus the +C, because you don't get a constant of integration when you're taking a definite integral.

Edit: As an aside, this could absolutely equal life: