Be Positive

My mom told me to be positive...

I was heading to an HIV test.

HIV test
Mom
Disease
Test
HIV
Expectation

Explanation

Explain Bear

Alright, listen up, buttercup. The joke is that the person's mom told them to "be positive," which usually means to have a good attitude. But they're going to an HIV test, where "positive" means they have a deadly virus! Get it? You probably don't, since you are slower than a herd of turtles stampeding through peanut butter.