Learn Icelandic: Mér leiðist í strætó.

The verb leiðast (to be bored) is an impersonal verb. In Icelandic, these verbs do not take a normal subject in the nominative case like ég. Instead, the person experiencing the feeling is put in the dative case, which is mér. So, you are literally saying something closer to 'It is boring to me.'

Why does the verb leiðist end in -st?

This is a middle voice verb. Many Icelandic verbs add -st to the end to express a state of mind, a feeling, or an action you do to yourself. When you look this word up in a dictionary, you have to look for leiðast (to be bored) with the -st attached, because the base verb leiða means something completely different (to lead).

English says 'on the bus', so why does Icelandic use í (in) instead of á (on)?

In Icelandic, you generally use í (in) for enclosed vehicles that you step inside, like a car, an airplane, or a bus (í strætó). You usually save á (on) for modes of transportation you literally sit on top of, like a horse or a bicycle.

Why doesn't the word strætó change its ending after the preposition í?

Strætó is a very common, everyday abbreviation for strætisvagn (city bus). Because it is a shortened slang word ending in a vowel, it is indeclinable. This means it never changes its ending, no matter what grammatical case is triggered by the preposition. You just use strætó everywhere!