discomfit
Meaning: to thwart, baffle
Usage: The normally cheery and playful children’s sudden misery discomfited the teacher.
foil
Meaning: to thwart, frustrate, defeat
Usage: Inspector Wilkens foiled the thieves by locking them in the bank along with their stolen money.
perplex
Meaning: to confuse
Usage: The unusual instructions perplexed the entire class.
confound
Meaning: to frustrate, confuse
Usage: MacGuyver confounded the policemen pursuing him by covering his tracks.
vex
Meaning: to confuse or annoy
Usage: My little brother vexes me by poking me in the ribs for hours on end.