Well.... I did NOT see ANY "aggression" either... I saw over-excited dog IN CONTROL... not calm, allowed to pull, and wanting REALLY bad to meet the other dogs, then getting REWARDED for acting out (the pets/rubs on his hind end as he's being "bad" - those will reinforce the behavior).
I think Hiraeth and Karennj both have some AWESOME advice for you to consider.
The harness you're using is allowing him to ignore your physical corrections (not that I saw any attempt at those). A poke in the ribs is an easy distraction/correction, and works independent of the collar/leash you have one. It doesn't have to be a hard poke, either... just a "hey! pay attention to me!" poke.
If he is over-the-top and reactive, a poke could also cause a redirection of his frustration to become a snap at you... so... even that might not be the best approach to start with.
My Recommendations:
1. As you leave the car, make him sit and wait, and calm down. When he's calm, proceed to the store. ANY tension on the leash, and you do a FULL STOP. If he doesn't relax... go back to the car and start over. He should figure out pretty quick that pulling will get him NOTHING. Staying next to you will be rewarded with getting closer to what he wants (the store).
2. As soon as he starts to 'key' on a 'target'... put him in a sit. You get between him and the 'target' - make him look at YOU. When he does, give him a CALM "Good boy", "thank you" and/or a treat. Walk away from the target and get him interested in something else (i.e. YOU and treats or pets from you). Keep him CALM. If he gets excited or anxious, leave the store and start over.
Be prepared to repeat going in and out of the store 2-4 times on the next visit. Yes, it will look goofy to the people there... but anyone who knows dogs will see you're in training and will totally understand, and might offer to help - i.e. if what Drago REALLY wants is to meet people and other dogs.... they might be a 'friendly stranger' to practice on - BUT - you MUST do it right! No pulling. Drago must wait calmly for the friendly stranger to come close, and for you to give a release cue (I use "go say hi"), so he knows it's OK for him to engage the person and/or dog.
Good luck, and keep us posted!!