Navy Seal Burpees.
Is there a more humbling exercise out there?
In my opinion, no. There isn’t.
I frequently use them as a weapon to shut up the loudmouths who come into my gym, bumping their gums about how great they are
10 navy seal burpees usually induces a sharp dose of reality into their quivering bodies.
What other exercises are out there that are just flat out painful and always avoided?
Bulgarian split squats
Thrusters
Battle ropes
GHR sit ups. Got the most painful headache ever from doing those in a CrossFit wod
It also set off my tinnitus. The coach thought he killed me or something
Proper tempo and peak contractions held for time.
Widowmaker squats
Dante Leg Presses
Doggcrapp: This is how I show someone the intensity they should be putting into every exercise and it really opens some eyes up quickly in the people I train. Either next quad workout or next time you dont feel like doing your normal leg workout, be true to yourself and take the number of plates you load up on the leg press for a hardcore 10 reps deep —cut it exactly in half and do one set of 50 reps deep. So if your bragging to everyone that you can do 12 plates on each side for 10 then guess what your going to be doing - 6 a side for 50. And you know what-- everyone
reading this can do the 50 reps, it just comes down to who has the most balls or not. You cannot lock your knees the whole set and you cannot rest your hands on your knees either. I try to get 25 first and then pause at the top (with knees slightly bent) and take 5 deep breaths and then get 10 more (5 deep breaths) and 5 more.(im at 40 now)…then the last 10 reps is pure tortuous hell…I usually do 3 reps (take 3 breaths)3 more reps, 3 more breaths, then 2 reps (3 deep breaths) and finally the last 2 reps=50 reps. Your legs will be absolutely destroyed and you better start
stretching or walking the next day is going to be an adventure. My best ever was about 3 years
ago I got 7 plates a side for 50 and i go deep (knees to armpits deep). The people that I have
seen who cannot make it to 50 are people who dont have the mental fortitude to take pain and
get pissed off or someone who starts to cramp. But youll learn alot from that one set, you will
learn the intensity it takes to approach every set on every other bodypart and exercise you do.
Bear complexes
Would offer more painful/humbling alternatives, but I don’t have any others because I avoid them too 
I have a very stupid/insane idea you should combine box jumps with the navy seal burpees.
1 navy seal followed by 3 squat jumps would make that look like a Zumba workout
Max effort 2.4km run
That is a soul taker. Without exception.
High reps on isolation moves where you get a strong stretch.
Like 20ish reps on the straight arm pulldown or pec deck or some RDLs. Holy shit it burns!
Shoulder killer?
By killer do you mean “likely to result in shoulder pain” or “likely to result in shoulder DOMs”?
Either way, it’s actually a core/hip exercises targeting the whole lateral line (serratus, intercostals, obliques, gluteals, peroneals)
The former. Looking at it I feel as if I might lack some integrity in my shoulder girdle to be able to do it.
I haven’t had any issues with it so far, but it does definitely require a good amount of output from the lats and serratus
Can’t beat classics like squats and deads
…back to back
2k row
I’m working on a #200 lb sandbag to bench exercise. Kinda like powerstairs in strongman.
I’m using some concrete pavers to stand on to create a deficit.
45 second rounds.
Glutes, hamstrings, low back, and traps all pumped. Forearms, too.
Kinda feel like a heavy KB swing.
AMRAP squats.
Cramp inducing, vomit producing, headache forming AMRAP squats. Divvy the stance, reps, rests how want, just don’t rack the bar until you’ve hurt your own feelings.
I just make them run. It is very discouraging when a fat man like me can have a better cardio than the shredded strong guy 
I have long legs and long femurs at that. Slant board barbell squats hit my legs like nothing else and as I’m sure many would agree working through a leg pump takes more grit than working through a biceps pump.
Take care not to go too hard initially as the patellar tendon might not be ready for it.