To be someone's "puppydog" means to be completely head-over-heels for them. Loyal, unconditional, and unwavering. Quite often, as in like the love of a puppy or dog, the person who is "puppydoggin'" might not be treated as well as they should be... but keep on forgiving, and adoring whomever they're in love with ...no matter what.
I keep hitting refresh on my email, hoping to see his name... man, I'm really puppydoggin' it.
A cutesey word teenage girls can say if they don't want to say butt sex.
Those two men are puppydoggin' it.