This is becoming common in upscale deli sandwiches and a major retailer even now makes "Garlic Mayonnaise" but you can DIY your own with version quick and easy at a lower price.
This makes 1/2 cup finished garlic mayo. I like to use it to dip my fries as well as use on a sandwich.
Depending on how "garlicy" you like your mayo determines how much garlic you want to add - for a subtle flavor stick with the 1/2 tsp garlic and 1/4 tsp lemon juice.
* 1/2 cup mayonnaise (I used commercially prepared from a jar)
* 1/2 - 1 tsp minced garlic (or 1-2 cloves fresh chopped up, depending on size of clove)
* 1/4 - 1/2 tsp lemon juice (I used RealLemon from a bottle - use fresh if on hand)
Add the minced garlic
Add 1/4 to 1/2 tsp of lemon juice on top of the garlic. Stir together and refrigerate at least two hours before serving to allow the flavor of the garlic to meld with the mayo. Keep up from 7 to 10 days in the fridge.