These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
That One Level: The sandpit levels in the first game. If your dune buggy went into the water, it took a very long time to sink - eating up a large period of time while your opponents got ever further ahead. Happily avoided in the later games with water hazards, as the cars would sink much faster.
ALL the desktop sportscar levels, due to so many falloff points and the cars moving far faster than most reaction speeds. MM1's finale, "Win This Race To Be Champion", is particularly heinous.
The real offender, however, was the Rufftrux levels. Not only are you likely to sink, but it's against an unbelievably stingy time limit. With all the sinking, it's very difficult to actually finish one. To add insult to injury, if you get 1st on all the races, this'll get you a Rufftrux level just after a Formula 1 race, which also qualifies for this trope. If you lost lives falling off the table (or onto the table), you won't be able to get them back (they're the prize for completing a Rufftrux level).
This is one of the main reasons the games have such a large fanbase; memorizing the course's tricks and finding specific ways of clearing them is a major part of the game's challenge.