killer sentence

"I Trust you" is a killer sentence...
when someone tells you "i trust you, i know you ll do(or not do)..." it really makes you do what you didnt want to do (or not do what you wanted to do)...
i badly wanted to play this prank on one of my friend...
i was about to do it...
but because she used the killer sentence: " i know you wont do it... i TRUST YOU(really stressing on the word trust)" i lost all enthu to do it...