If he's your best friend of 14 years and you're both men, just be straight with him? Not straight like insulting him but give him a logical explanation of what he's doing wrong, humbly.
I have found that explaining some guidelines about women works very good because most times they make sense. My friends never were casanovas or anything, just regular guys and I never was/am in a big player position but since I've told them some guidelines they realize it's logical and follow it and thus I have myself good wingmen, and I can be a good wingman myself.
Although I could understand that if he thinks he's such a casanova he could laugh at your tips or something, but in that case how about you say that he's stealing your thunder and you want him to keep low profile one night. Since he's a big playa he shouldn't have a prob with that, and maybe after the night he will be interested in your pua abilities and ask/accept some guidelines.
just my 50cents, hope its useful
