Scars.

...a circular one on one thigh about 3" from a spider bite.

They are your  pals,  after all.  Does anyone have
siblings who  have  attacked  them  when they were
younger?  A one-inch scar  remains from that (just
below the hairline).  Two skating-related injuries
are still visible,  such as  the upper lip (from a
10-foot half-pipe) and  the right knee.  Any other
scars are  internal and can't be  seen (that would
explain a frequent bloody nose and...).