the literal definition of this phrase is referring to the bottom of a bag of chips. the slang definition of this phrase was brought about by an instance of a person purposely opening a bag of chips from the bottom and then claiming that it is normal/common practice when it is obviously not common practice. ever since that pivotal moment in history, anything that is uncommonly weird and/or eccentric can be referred to as “bottom of the bag”. this phrase is synonymous with “that’s sus” (as in “that action is suspect”)
Tom: did you see Spike get some hand-sanitizer and use it style his hair?
Jerry: Yeah, that was kind of Bottom of the Bag for him to do that
While our lifespan is the number of years we will live, our healthspan is the number of healthy years we will have and our sexspan is is the number of years we will continue to be healthy enough to continue having an active sex life.
A lighthearted reaction upon receiving disappointing news of some sort. Usually something that isn't a particularly a big deal, esp. when it primarily affects someone else - sort of a mild schadenfreude. Sometimes doubled or tripled, and possibly said in a sing-songy voice for added comedic effect to imitate a muted trumpet, which is how the meme originated.