He proved my point so fast

Recently I went to a wedding, and a man in the wedding party had chatted with me off and on during the wedding. He was nice enough, someone that I would engage with amongst friends (like if the bride I knew hosted a party or something) but not really someone I'd date. I noticed during the wedding he was drinking quite a lot, enough that even the bartender told him to slow down (I watched him pound back two drinks in less than 20 minutes after the cocktail hour began, and the bar tender told him to wait before he'd serve him a third drink. He drank more during the rest of the reception). Said some other stuff in conversation that just came off as someone who needs to spend a little more time getting their shit together. At the end of the wedding he asked me for my number. I need to practice how to say no because I shrugged and gave him my google number...he also caught me while I was on my way out the door and trying to go catch my train home, so perhaps I thought it was just be faster to give him a number and run. Should've just given him a fake. Bleh, whatever, maybe he'll forget right?

Today he finally followed up and asked to go out. I was with some friends and when I got the text I was like 'oh no' and explained my concerns, esp the drinking. At first they tried to be like, well it's his friends wedding (he knew the groom) and maybe he just wanted to party etc. and I was like ok sure, I get it. I go to my friend (the bride)'s FB page to pull up a picture of the guy and his profile pic is literally him double fisting 2 alcoholic drinks. The jokes write themselves. Immediately my friends were like "oop, ok, I understand what you're saying now".

I'm definitely not going to go out on a date with him because I'm just not interested, although if anyone has any tips on how to decline giving someone my number in the future that would be great...