Slick - done in a very impressive way that seems to need very little effort; a slick person is clever and good at persuading people but probably not honest or sincere. Example - "They ran a very slick promotion campaign, you must admit."
Whirlwind - something that happens very quickly and unexpectedly, so that the people involved have little control of what happens and how they feel Example - "They are married already? Talk about a whirlwind romance!"
Lump sum - single payment of money, as opposed to a series of payments made over time; asingle sum of money that serves as complete payment. Example - "When you retire, would you like to receive a lump sum or would you rather have regular income?"
To rain on someone's parade - to spoil something for someone; to do something that spoils someone's plans. Example - "I hate to rain on your parade, but you know you are not allowed to have friends over."