Answer: thatll

AnswerCrossword Clue
THATLL

"... do!" (words of acceptance)

THATLL

".. Be the Day"

THATLL".. be the day!"
THATLL

"Like ... ever happen!"

THATLL
"... be the day!"
THATLL
"... do!" ("Stop it!")
THATLLBuddy Holly's "... Be the Day"