Learning a second (or in this case third) language when not a child can be a challenge. When I started learning Spanish, I somewhat subconsciously decided to stop being afraid of making mistakes, and just speak as much as I could. I never had the balls to do that during my years as a French learning (and very awkward) teenager, and now my broken and limited French only pops up in absolute emergencies. (Which is another story.)
This decision is what I believe to be the very reason why my Spanish worked out ok pretty fast. It did however come with the risk of making an absolute fool of myself (which I already have a decent talent for), which is what I will be so generous to share with you in this post.
#1
I once walked into a fancy store and asked for Barajas (the Madrid airport) instead of rebajas (sales). The clerk pointed politely in one direction, but I’m still not sure towards which of the two.
#2
After making plans to fly from Quito to Cuenca (Ecuador), they canceled my flight, and I told a whole bunch of Ecuadorians at my Spanish school that my flight was cansado (tired) instead of cancelado (canceled). Some saint had mercy on me and corrected my mistake, and I will never mix up the two again.

#3
For a while, I sometimes greeted people with chao (goodbye) instead of hola (hello), because I thought Spanish was like Italian, where ciao means both hello and goodbye. I cannot have seemed like a friendly person.
#4
I once told my Spanish teacher that I was fácil (slutty) when trying to explain I am not a drama queen. This word usually means easy, but apparently not when you say it about yourself. She chuckled before telling me never to repeat that sentence.
#5
Being the only foreigner among a group of locals in Madrid, I once somehow communicated that my husband wakes up horny every morning. I was trying to say that he is happy and full of energy, but the sound level of the crowd’s laugh had me understanding pretty quickly that I had said something cringe-worthy. To this day I have no idea what exactly was my mistake. Still makes me cringe though.
#6
One of my favorite Spanish 80s hits (yes, it is a thing) has a line going (…) y cuentos chinos (Chinese tales). Just recently I realized that for years I have been singing (and I have been singing it A LOT) cuento chinos; I am counting Chinese people. I always thought that part of the lyrics was a bit weird, but then again, there are a whole lot of Chinese people in Madrid.

#7
In the very early stages of my Spanish, I was walking around the capital of Ecuador looking for an ATM. Not having any idea how to say that (and this was before smartphones), I took a chance and asked a random guy for a mini banco. I now know oh too well that a mini banco simply sounds like a very tiny bank. He did however understand what I was searching for and pointed me in the right direction, but not before having pronounced cajero (the actual word for ATM) extremely clearly articulated and making me repeat it three times. I will forever remember you, my educating friend.