re: 3 months to beach vacation - advice on getting beach bod ready

If you are 5'9 165 lbs at 25%+ bf you have a lot of work to do my friend.

You need to
1) Gain a lot of muscle
2) Lose a lot of fat

You wont be able to gain as much muscle in 3 months to make a huge difference. Id suggest a 500 calorie deficit every day, minimum 30 minutes a day walking(with some hour+ days mixed in). Obviously you need to get on a lifting plan that you can feasibly manage 2-3x/week.