It is said that if we refuse to donate someone who has come to ask for donations, then our Punya is lost.
What are other ways, as per Scriptures, which make us lose Good Virtues?
There must be many ways of doing so. Here are few of them from the Atri Smriti:
To cleanse the teeth with a finger, to eat unmixed salt, and to eat earth is equally sinful like eating beef. (310)
[To live under] the shade of a Kapithva-tree during the day, [to take] curd in the night,[to live] under the shade of a Sami-tree, to use a cotton-reed for cleaning the teeth, robs even Vishnu's prosperity (311).
The Sun [when seen at the rising], the wind [of the cremation ground], the water on the finger-nails, the water in a pitcher touched by a cloth at the time of bathing, the dust of a broomstick, and water sprinkling from the hairs, destroy the virtue acquired in the day. (312)
All the above methods are effective ways of losing punyas specially the ones highlighted. :D