It is extremely hard. If that teacher was perceptive enough, he/she could have detected a bullshit tick. Well... for all of my tutors, I see that their tick have a unique style to it which MAY need practice to emulate. So to completely emulate a person's tick, you must exert the same amount of force on the page equivalent to how the person would. (helpful with lots of luck on your side)
Also there are different types of red pens, some have more intensity than others. blah blah blah
Conclusively, I think putting a tick on the paper in disguise is hard like a rock
Bold part 1: yes but it is not hard to 'copy' their style. I mean after all you are trying to copy one tick not preform a handwriting analysis on them.
Bold part 2: ofc you need to practice it lol. when i copied my parents signature, I filled up about 2 and a bit pages before i signed the real thing.
Bold part 3: not really. I would think that most people use the same amount of force to get the ink on the page. pens are designed to be "effortless" so a weaker person would need the same amount of 'force' as a stronger person but the weaker person will feel like they're putting in more effort relative to the stronger person
Bold part 4: most teachers/tutors and whoever else use a water based ink with a steel tip (you know the higher more pricey ones, that leave a "dent" in the page) such as uniball eye micro or the 150 range (0.5) [i have a special talent for pens] so ideally not that hard to copy. Furthermore; you want to do a tick with "confidence." most people leave their pen on the page for the duration of the tick however you should be letting go at about 1/2 way through the tick
NOTE: i do not agree with cheating but rather I am explaining that unfortunately it can be easily done.