"NO!" is a complete sentence.
Example: "I broke my glasses and it will cost XX to have them repaired. I need the money." Your answer: "NO. I paid for the glasses first time around. You worked this summer and can take the $$ out of your account. Try to be more careful."
"I lost my calculus book and need $$ for a new one." "NO. I paid for the first one, you get to pay for any losses. "
"I lost my meal card and had to eat out and need money." I am sorry about you losing your meal card and it is a good thing you had enough money to eat out. I am not sending you more money. Please be more careful in the future." (If he has enough $$ for cigarettes he can find a way to get food!)
And when his summer money is gone, NO to more spending money is a complete sentence.
"I told you not to smoke in the House. You are in the window and that is in the house. Put it out and respect the rules and my trust in you, please. Thank you." followed by not answering in further discussion.
No is a complete sentence and you are not obligated to discuss everything. Some things are not up for discussion. Your rules. Your money. Your house. Period. (and BTW when he cries 'unfair' tell him life ain't exactly fair.)
Addicts are great manipulators and so are many codies. You can choose to be manipulated and you can choose to respond or you can choose boundaries that you can stick to and allow the addict to face the consequences of their actions. Up to you.