From fairest creatures we desire increase,
That thereby beauty's rose might never die,
But as the riper should by time decease,
His tender heir might bear his memory:
But thou contracted to thine own bright eyes,
Feed'st thy light's flame with self-substantial fuel,
Making a famine where abundance lies,
Thy self thy foe, to thy sweet self too cruel:
Thou that art now the world's fresh ornament,
And only herald to the gaudy spring,
Within thine own bud buriest thy content,
And, tender churl, mak'st waste in niggarding:
Pity the world, or else this glutton be,
To eat the world's due, by the grave and thee.
Two archaic words are used here. “Churl” in Shakespeare’s time meant “peasant” and also “miser”.  That he uses the adjective “tender” would make this seem like an  oxymoron , a contradiction in terms. We can assume that the tone is teasing rather than insulting. 
 “Niggarding” is the origin of the modern “niggardly”. and also means miserly. So the line can perhaps be loosely paraphrased as, “dear careful one, you’re wasting your beauty by denying it to others.” Or better, “by denying others your beauty you are actually wasting it.”
Sonnet 1