The phrase "huge pat" means giving someone a big and enthusiastic slap or tap on their back or shoulder to show appreciation or recognition. Full definition
Huge pat on the back to Marshalls for carrying this amazing Calvin Klein one for supa cheap (lynzyandco.com)
So true, Jessica, when something that we create is really, really good, than kudos, give yourself a huge pat on the back! (kitchenbelleicious.com)
But in the end the Gunners did win at a canter and the forgotten man Olivier Giroud can give himself a huge pat on the back for his part in the three points. (justarsenal.com)