Part of you wants to call an ambulance; part of you wants to run away; and part of you wants to crack up.
From there we see Biden start to crack up—perhaps caught off guard by the unexpected compliment.
After hours of this—literally—men begin to crack up, and a class of 100 can shrink by 10 percent in a few minutes.
"split, opening," 14c., from crack (v.). Meaning "try, attempt" first attested 1836, probably a hunting metaphor, from slang sense of "fire a gun." Meaning "rock cocaine" is first attested 1985. The superstition that it is bad luck to step on sidewalk cracks has been traced to c.1890. Adjectival meaning in "top-notch, superior" is slang from 1793 (e.g. a crack shot).
[all senses are ultimately echoic; narcotics sense fr the sound of breaking crystals or the cracking sound the crystals make when smoked]