If it's tough in terms of the scale or effort required,

Herculean:

1. Of extraordinary difficulty, might, power, size, etc.; of or relating to Hercules in size or strength.
2. Requiring a huge amount of work, as a Herculean labour, a Herculean task.

If it's tough in terms of its unsavouriness,

odious:

1. Arousing or meriting strong dislike, aversion, or intense displeasure.

You can find words similar to either sense by using a thesaurus.

If it's tough in terms of the scale or effort required,

Herculean:

1. Of extraordinary difficulty, might, power, size, etc.; of or relating to Hercules in size or strength.
2. Requiring a huge amount of work, as a Herculean labour, a Herculean task.

If it's tough in terms of its unsavouriness,

odious:

1. Arousing or meriting strong dislike, aversion, or intense displeasure.

You can find words similar to either sense by using a thesaurus.

Edit: As per the OP's comment,

Trying to talk politely with a rude person is an odious task

or, using a tamer synonym,

It is very challenging to talk politely to a person who is rude to you.