I've never had "jalapeno mayo" -- but it sounds delicious!!
The easy way without making your own mayo is to use 1/2 cup mayo, 1 jalapeno with seeds and membranes removed use 2 if you feel particularly suicidal or use serano peppers if you really want to get lit up. Use your blender or one of those mini food processors that are so handy and only cost about $30, buzz the pepper with a tsp of lemon juice then add the mayo and maybe some parsley or cillantro and pulse till blended. Good on burgers, sandwiches, making pimento cheese and fish.