trifler

/ˈtraɪflər/
noun
  1. A person who treats serious matters lightly or without proper respect; someone who wastes time or acts frivolously.
    • The old professor had no patience for triflers who came to class unprepared.
    • She was dismissed as a trifler who never finished any project she started.
    • Don't be a trifler with your responsibilities; your team depends on you.
What does "trifler" mean? | whatsthatwordmean | whatsthatwordmean