How tall is your avatar? If you script, you know that while llGetAgentSize() claims to tell you, it isn't as accurate as getting the avatar's bounding box with llGetBoundingBox().
I am very amused that there's no way via script to guesstimate how thin or fat an avatar is. llGetMass(), llGetAgentSize(), and llGetBoundingBox() all assume default values for an avatar's x and y dimensions, and so any variation in their results is based entirely on the height of the avatar.
Add the following script to a prim and touch it to see how tall your avatar is.
key avatar = llDetectedKey(0);
string name = llDetectedName(0);
list BB = llGetBoundingBox( avatar );
vector size = llList2Vector(BB,1) - llList2Vector(BB,0);
integer feet = llFloor( size.z * 3.28084 );
integer inches = llRound( (size.z * 39.37008) - (feet*12 ));
string meters = (string)size.z + " meters";
string us = (string)feet + " feet " + (string)inches + " inches";
llSay( 0, name + ", counting your shoes you are " + meters +
" or " + us + " tall.");