To be spindly is to be so tall and thin as to be stilt-like.
(Photo of a Black-winged stilt by Francesco Veronesi)
Tall and thin aren't bad things to be:
(That's President Lincoln)
though it can be a nuisance if the wind catches your folds of sagging skin and blows you over.
The main problem, however, is that if you're spindly at this time of the year then people will suspect you of being a spoil-sport.
Thing Not To Be Today: spindly. This word comes from spindle, a stick used for spinning wool into thread. It comes from the Old High German spinnala.