The title, "Roshambo," is another name for the hand game rock-paper-scissors, and the poem opens with a small result: stone beats paper. In the game, that's an ordinary, trivial outcome. But the speaker doesn't leave it there. Right away comes a second move, "as I oblige myself with six / bottles of wine," and the two events sit side by side as if one led to the other.
The poem never says what the speaker feels, which is part of its effect. The word "oblige" is the key. It makes the drinking sound like a duty or a forfeit, as though the speaker lost a game and is now paying up. Yet the speaker is also the one doing the obliging, so there's a sense of making an excuse for indulgence. Six bottles is far too much for a punishment.
The mood is wry and a little dark. It's funny on the surface, but the dry tone also hints at loneliness or restlessness, since the speaker seems to be playing a game and drinking alone. The poem leaves that for the reader to decide.