I know I've shared this verse before but it may help some to see this again in a slightly different light.
Christians are no strangers to getting upset and finding reasons to complain! It is sad to see this, and I have to accept I've done my share of complaining too! But two things helped me and still help me to seek to turn away from a "complaining spirit."
First - Consider Jesus facing an unjust trial and not saying a word of complaint for the way He was treated. Isaiah 53 and the Gospel accounts both emphasize that under trial and brutal attack both with words and fists - He never said "a mumbling word!" He was quiet and He took the abuse knowing that He was facing this cruel treatment on our behalf. He loved us and still does! So, any time I'm ready to complain, I just remember what Jesus went through and I learn to accept ill treatment from others without getting so upset.
The old song, "Follow Me," has these words, "I traveled down a lonely road, and no one seem to care. The burden on my weary back was much too hard to bear. I oft complained to Jesus how folks were treating me; and then I heard Him gently say to me, 'My feet were also weary upon the Calvary road, My cross became so heavy, I fell beneath the load. Be faithful weary pilgrim, the morning I can see. Just lift your cross and follow close to Me."
Second - When I face unpleasant situations and people, I find taking time with Jesus changes my focus and He lifts my spirit. I often quote this little ditty which I hope will bless you too:
We mutter and sputter, we fume and we spurt; we mumble and grumble, our feelings get hurt. We can't understand things, our vision grows dim; when all that we need is communion with Him!"
Take your mind off your woes, and "turn your eyes upon Jesus. Look full in His wonderful face. And the things of earth will grow strangely dim, in the light of His glory and grace!"