LOL...this past February when my youngest was at OCS, my other Marine son sent his little brother a package addressed to his platoon sergeant. In it was a box of care bear valentines and a note asking the sergeant to please have this candidate to distribute them to his squad.
It just happened that day the mail was distributed by the platoon commander. Big brother got lots of laughs when he found out what happened!
If you do send a letter, make sure you mention the rude behavior of the DI and how you think he isn't a very proper "soldier".