Slippery fingers are a result of eating deep fried or french fried food from a tin, trying to use a cursed can of grease, or trying to apply or #dip a cursed potion of oil. They last up to fifteen turns.
When your fingers are slippery, you drop any non-cursed weapon you were wielding (which can be problematic in a shop). If you are not wielding a weapon, or you are wielding a cursed weapon, your rings may slip from your fingers. Applying a towel effectively cleans your fingers. Putting gloves on does not remove or cover this effect, due to forces of physics yet unfathomed. The lesson here is to watch exactly what it is you are eating/applying, as slippery fingers can very easily lead to a swift death if said tin or grease was used out of pure necessity.