How can i say goodbye to my teacher?

My teacher was just covering for a teacher on maternity leave this school year and he was my favorite teacher ever. he just got out of college so he thought like us. i didn't see him as the hot 20-something year old. he was kind of like a friend. he wouldn't point us out in class but come talk to us after. he was also very technological so he made us like a class comic and we would play games with us for every occasion like we had Christmas Extravaganza and we called Easter, E-sta and held up three fingers to make an E. he would diss kids in class (but wouldn't hurt them) and would call teachers by their first name. He's not very mushy and comfortable with hugging and stuff like he called "Puberty Talk." the "Nitty Gritty of Life." but me and my friends really want to congratulate him for being an awesome teacher without like making him feel uncomfortable because this is last year. what should we do for him?