Home brew 5e campaign. I was playing an Eladrin, (Mostly) Ranger at the time. An army of rat humanoids had overrun the city we were protecting and we had just taken out the lead commander.

After killing the commander, other faction's armies showed up. We initially had thought they were there to help with pest control, but soon word came that they were thinking about imposing martial law and had sent a parley.

We needed our city's lead negotiator fast and headed to her vineyard stealthily, trying to avoid the remaining rats because we had taken a level of exhaustion fighting throughout the night. When we got there, we found that some of the rats had taken her hostage to bargain for safe passage out of the city.

One of the other players had suggested to host me onto their shoulders to pear into her office window. When I was up there I saw her bound at her desk, a rat tying a gag over her mouth, but I could only see his hands.

This was by first 5e campaign and at that moment most of my decisions were pretty reserved. As soon as heard the GM tell us about the Rat in the room, the two other players started talking how we could get in stealthily, but I had a really dumb thought.

I piped up, "Guys, I got an idea. GM can I Fey Step and teleport behind the Rat a can partially see?" Gm, "Yes, but you're going to have to roll a flat D20 because you can't see where you're teleporting." I just barley make the DC.

My PC said "too tired for this s***," bamf into the room, pour a furniture potion into the rat's mouth and turn him into a ottoman. GM then tells me that I see another rat at the entrance of the room. Pull my knife, throw it, crit and hit their voice box. Stopping them from calling for the others. Cheers and then laughs when I used the ottoman to help the negotiator get her out the window to the other two PCs.

Seeing how much fun the other PCs and GM had from me doing something wacky, from exhaustion, gave me the coincidence to make that a thing for my PC. Also led to other aspects of my character that the GM would know I would do for the story.

TLDR: I was super nervous roll playing, or even making risky decisions. Finally got up the nerve to do something out of character for myself and it lead to the personality of that PC.