First and foremost, the only clear-cut answer one might obtain on this subject would be from the DM running the specific campaign in question.  The classification of actions as lawful, chaotic, good, or evil and the relative magnitude of the action relative to the classification (i.e., the action is evil, but just how evil?) is based entirely on the ethos of the particular religion, culture, details of the outer plane which is the source of the alignment, etc.  That said, detailed knowledge of these things is generally not necessary.

More important is understanding why ‘falling from grace’ is included in the rules in the first place.  Like most other character restrictions and limitations in the rules, this one is included to help enforce balance between the character classes.  Paladins are granted a number of special abilities that are of significant advantage.  Immunity to fear and disease alone are high order advantages.  These advantages are offset by a number of equally strict limitations such as the single lawful good alignment.  One might fancy a Paladin views (or should view) strict discretion and application of great power to be as much a measure of ‘power’ as the effects of its use.

The methodology behind the mechanics, however, must always be balanced against the reason for playing the game in the first place; to have a fun and meaningful game play experience.  The Paladin’s ‘fall from grace’ restriction/consequence is purposefully left vague and is intended more as a threat or failsafe than as a rule to be implemented.  That said, use it as such.  Certainly actions deemed as utterly evil should be met with immediate expulsion from the ranks of the chosen.  However, assuming the player is attempting to stay in the spirit of the game, such blasphemy will be very rare.  Most potentially ‘damning’ acts fall into a gray area of lesser sin.  Continuing onward with the assumption of a well-intentioned player, a good dm should ‘guide’ the paladin in such a way as to bring clarity to the ‘correct’ path of behavior when deviation has or is about to occur.

There are several typical methods to impart this ‘wisdom’ upon the character and these are often most effective when used in combination. Providing a simple verbal warning of a sort is the more kind of these tactics.  This may be a direct ‘dm to player’ dialogue or something a bit more subtle and ‘in-game’.  “You are suddenly blinded by an intense light.  A moment later the glare from the noon sun striking the surface of the lake ahead subsides with the passing of a cloud, but you can’t seem to shake the feeling you have been given a sign…”  Alternatively, a post-action penance of some sort may be mandated by a high authority local theocrat, or demanded from a brief encounter with an ‘angel’ or other minor servant of the cause.  A quest to find some sacred artifact and a hefty tithe to the local order will often curb even the most ignorant of players.  The severity should fit the score so to speak, but a few of these instances are usually enough to make the point.  Ultimately, the actual act of stripping the character of Paladin status should only be undertaken when multiple warnings and/or penalties are ignored or as a last resort of sorts in any case.

How do you decide when a paladin has fallen from grace in DnD 5e?
I am curious if anyone uses a skiing helmet for winter biking? Would this be safe? Are skiing helmets designed to protect you from the same kind of accidents that you would have on a bike?  

My thinking is that a ski helmet would:


Help to keep your ears warm
Would fit well with ski goggles (which fit poorly with my bike helmet)
Not have air vents in it which make you cold in the winter

