Once I read the wrong reading and the presider interrupted me and showed me a new reading. Thankfully it was only a weekday mass and there were only three other people there.
Back when I was an altar server, I’ve made tons of mistakes, or hiccups, if you want to call it that. I once hit the censor against the table in the sacristy and the charcoal flew and burned a hole in the new floor the pastor made a few weeks before. I remember he was furious and I ran away after mass. I was only into my first few months serving and didn’t have much experience with the incense yet.
When I was still an amateur, I was serving the 11 p.m. mass on New Years Eve, a mass of Thanksgiving, and I fell asleep during the Eucharist prayer. We use a gong during Transubstantiation and ring the bells when the priests kneels in adoration. I was wearing the metallic altar server cross and that hit the gong and made a pretty loud clang during the prayer, it surely woke me up though
There was one year when during our annual 40 Hour Devotion, we had a shortage of altar servers during the Eucharistic procession, and I was the cross-bearer. I was still young and never lead the procession before (around the church three times). I walked so fast that I was already on the 2nd lap (if you want to call it that) before the Bishop even left the altar with the monstrance.
Another time, this time when I was maybe a bit more experienced with the incense, I went out of the sacristy (we keep the smoking censor in the sacristy when not needed to limit the smoke in the church) at the wrong time and stood there awkwardly till Father said not now.
During one funeral, I was the only one serving, and I exited at the end with the cross, without waiting for Father to say the final prayers.
These are the only ones to come to mind. There are hundreds of tiny mistakes I made as an altar server that are not even worth mentioning.
. It was quite funny, there were a few quiet chuckles.