You need a second "session 0"

The problem, as I see it, is that the other player decided to play a different game to the one you all agreed to. You say in your session 0 that you all agreed to a heavier story, and yet this other player is not doing that, even though you are.

Playing a gloomy character isn't always a "drag to be around", even though some may perceive it that way depending on the kind of game they're after; it can be very interesting to play a "miserable character" if this was agreed up front, which it was. Conversely, I wouldn't find any of this other character's "jokes" that funny even in a more lighthearted game, so I also don't think that he's all that fun.

To quote a comment by @Chepelink:

There is a fine line between happy-go-lucky and a bully that thinks he is being funny. For your question, I think Chirp is [leaning towards] the second type.

A statement with which I wholeheartedly agree.

Of course, everyone has their own ideas of "fun" and "interesting", but I just wanted to point out that just because one person thinks something is "fun", doesn't mean they're automatically right and can go unchallenged on that; indeed, aligning differing opinions on what fun means is partly what session 0 is all about.

As for whether this is up to the DM or not, I'd say no. I think what you need is another "session 0". You mentioned that you've already aired your feelings and that whilst they were met with sympathy, nothing has changed. This second "session 0", then, should contain either actions to how the game will become more "heavy" (read: the other player plays the tone they originally agreed to play) or re-evaluate the tone (i.e. lighten the tone up, but at least you know that's what's happening now rather than playing a different tone than the other player).

I say to your players, something else is the way to go. Fake it til you make it. Give 'em the old razzle dazzle. Sell the sizzle.

You can't speak orcish, but maybe you can fake it with the best of 'em. Whatever the orcs say, nod, shrug, moan, make a vaguely orcish grunt, point to your mouth and move on. Or maybe when an orc says something to you, nod, try to make a sound that sounds like a sound the orc just made, and keep moving.

Some props might help. Wrap a bloody bandage around your lower face, and fake an orc with a ogre-size toothache. Maybe some real orc blood will help sell the smell. Maybe drag a "dead" halfling along like you're taking the body to the boss.

A little charisma and maybe some proficiency in performance and deception and some luck is your best bet. Any other spells you got, use 'em -- suggestion, charm person, friends, enhance ability, could all be useful.

A distraction might help. Illusory elves attacking on the other side of camp maybe. Elves, man, orcs hate 'em. Or maybe an ally lobbing a fire arrow into the other side of camp might cause a distraction. Setting fire to the tents is always an option worth considering.

And when the jig is up, and they're getting wiggy on you, you can point in the distance, wide-eyed, make some orcish grunts, and heel-and-toe it out the door. Haste might be helpful.