Some great stories in this thread!
Bear in mind I'm not Scottish or Irish - I'm Basque and I've lived my Celtic supporting life in a very different way, over a thousand miles away. I have a couple anyway:
1) When my friends and I were teenagers and we went to Salou in the summer for the first time, must have been 2006 or so. I wasn't even a proper Celtic supporter yet, I just liked the team. My pals were into football as well and they liked Celtic too so we ended up buying a few of those knock-off Celtic shirts for 10€ each or so (I know, I know) so that all of us would go to the beach in Celtic shirts.
The abuse we had to endure was eye-opening! Six or seven fucking kids in Celtic shirts and five minutes in a fat bastard had already stuck out his full upper body out of the car window to shout shite at us, many more British tourists gave us funny looks, one guy even shouted "God save the Queen!" at us ffs
We didn't understand it completely yet (and it's not like we were in fucking Govan, it was Catalonia and we were gonna wear whatever we wanted) but we kinda liked it (because no one took it further than that, I must say) and it was one of the things that turned me on to start with what is complete love now: arseholes hated Celtic, so I instinctively grew more attracted to it.
2) This is not a specific story, but living outside Scotland/Ireland/UK the amount of times you get to see people wearing Celtic apparel is limited... but fairly consistent! Basque people like Celtic more than you'd expect and you'll always end up seeing a hooped shirt here or there. You know when you go on holiday somewhere big and you know you'll eventually spot someone wearing the hoops? Well, it's like that here too. That moment when you come across someone in the hoops and you whisper "mon the hoops" or something like that and you get that look of complicity from someone who didn't expect that, I've always enjoyed it. It's a two-way street too: last Saturday I visited Bilbao wearing a Celtic tee (plain grey one, grey logo, so you had to pay attention to notice it) and two different guys said "aupa el Celtic!" to me totally unprompted. Love it every time.
and 3) I'm an Alaves season ticket holder as it's my hometown team, and in 2017 it reached its first ever Cup final, against Barcelona of all teams. They scheduled it on 27th May which was... yes, you guessed it, the same day we were playing the Scottish Cup final against Aberdeen for the first invincible Treble ever.
I was fucking devastated that I couldn't watch the Hampden match, but I had a ticket for Vicente Calderon (the last official match ever played there, too!) and I wasn't gonna miss it to watch our match on a shitty streaming or so. I googled for Celtic bars in Madrid but my friends insisted I wasn't gonna miss the fanzone so I settled on watching it on the phone there. However with all the people packed in the fanzone, reception was terrible and my data wasn't working properly, so I ended up following the match combining twitter and a football app. I remember that game way more vividly than many matches I've watched in person!!! Hayes' goal, Armstrong's belter, Stockley's elbow on Tierney... I followed the whole match in agony while people were having fun and drinking around me (don't worry, I was drinking too). Then Rogic scored on the 92nd, a minute or so later the notification reached my phone and I went fucking crazy, "we've won it!!! we've won it!!!" a guy looked at me like I'm fucking nuts and said "relax, dude, it's actually a few hours until it starts"
A few minutes later I spotted a guy wearing a Celtic shirt in our fanzone (see number 2 above!) and I just went straight to him, hugged him and told him WE FUCKING DID IT! I think I had to explain to him afterwards
I don't think I've seen a goal repeated so many times as I watched that one, my battery ran dry well before my second cup final of the day started! We got an Invincible Treble that day but sadly I didn't get a personal cup double that night, although that is not a Celtic story and thus I'll leave it at that...