CAN THORNMAIL HAVE GREVIOUS WOUNDS ALREADY
has 10% lifesteal and 100 AD (not including armor pen)
has 100 armor
has 
deals 50 damage (50% damage reduction due to armor)
deals 35 damage to from
then heals 5 back
now lets go to late game
has 20% lifesteal and 300 AD and lets assume 100% crit with infinity edge (not including armor pen)
has 400 armor
has
deals 150 damage (80% damage reduction + 250% from crit)
deals 190 damage to from
then heals 30 back
Notice crit deals a lot more damage than it looks like it should
Ok now for the broken part Lets add resistances
has 10% lifesteal and 100 AD ( including armor pen 7% from masterys and 13 magic resist from runes)
has 100 armor
has
deals 57 damage (50% damage reduction due to armor)
deals 31 damage to from (11% magic damage reduction)
then heals 6 back
late game
has 20% lifesteal and 300 AD and lets assume 100% crit with infinity edge (including armor pen 7% from masterys 35% from last whisper 27 magic resist from runes))
has 400 armor
has
deals 240 damage (32% damage reduction + 250% from crit)
deals 150 damage to from (21% magic reduction)
then heals 48 back
if each champion had 2000 health
would die after 9 auto attacks
would kill herself after 17
= 265 damage + 100% critical +20% lifesteal without boots.
synergize
) against a thornmail. When you see one, its usually on a 250-300 armor tank, 3k+ HP. Think about that, thats 15% of the ADCs damage pre-mitigation. What that means is that the ADC will take around 100 damage for hitting you with a crit on a basic attack, not counting your bonus armor damage, which would be 250-300x0.25, or 63-75 more damage.
+
