Combine pineapple and jalapeno slices in a cocktail shaker and muddle. Pour in tequila, pineapple juice, lime juice, and orange juice. Fill with ice and shake until well combined. Set aside.
Place tajin on a plate. Rub one side of glass with lime slice and roll in tajin. Strain margarita into the prepared glass and garnish with pineapple slice and jalapeno slice if desired.
