Can I put cologne in my bag and they can check in my bag so i can bring it? since its 4.2 oz

You can put it in your main suitcase in the hold of the plane but not in your hand luggage. At the moment any liquids over 100 ml will be confiscated. In fact some flights with have it anyway. It is the same rule for anyone.

you can put liquids in a checked bag no problem. if you want to carry it on, seal it in a plastic bag first.

http://www.tsa.gov/311/index.shtm