@JeremyECrawford
My friends were discussing if temporary hit points have resistance to what ever damage resistances you have. Far ex. A teifling takes fire damage and has armor of agathys does it take the resistance to fire from the teifling?— LilD00bie (@AndrewDerp) March 14, 2018
Resistance applies to any damage of the appropriate type, and does so before anything else happens.
Temporary hitpoints work exactly like normal hit points, except they are deducted first.
If you take Fire damage, but have Fire Resistance, you cut the damage in half, and deduct the result from any Temporary Hit Points you may have, and then deduct whatever is left over from your actual current Hit Points.
If you have 20 hit points, 10 temporary hit points, Fire Resistance, and take 41 points of fire damage, your resistance cuts that down to 20 points, your temporary hit points absorb 10 points of damage, and the remaining 10 points are deducted from your actual hit points, leaving you at 10 HP with 0 THP.