If you want to catch a cold over night there are various tick to it and can easily do that. Just getting wet in the rains for a longer time can easily catch cold. If it is not raining and you want simpler idea then just go to the bathroom and take a nice shower for an hour and wet your hair. Surely you will get cold. Even if this fails then you can take this wet hair and stand in front of the Air conditioner or you can make use of the fan in full speed. Drinking very chilled soft drinks or ice slush can also cause cold overnight.