If you don't regularly put menthol on your nuts, then it will feel like it burns the first time. But you get to a point where your day doesn't feel complete without mentholated nuts if you begin applying it daily... Just sayin...
Question about your groin (and this is serious), but where exactly does it hurt? I ask because a lot of people say things like "I pulled my hammy last night" but they're still walking around no problem. I've seen people refer to their quad as their hamstring, tell my they pulled there back out that morning, etc., so any time I see someone say they did something to a muscle, I'm a bit hesitant. Don't get me wrong, I'm not saying you're dumb by any means, but I thought I injured my groin a few years back when in fact it was a hip flexor strain that simply needed a little adjustment at the chiro, a little psoas massage (most painful thing ever), and i was back on the field a couple days later. Can you describe where the pain is? If it starts around the front of your leg (pelvis area), then you may just need a little work on it.