1. I have 4 room mates. I tell them I take really long showers cause they’re so relaxing. First I repeat this to myself until I believe it. (in my mind “long shower” = PE, I don’t think about going to PE, I just say in my mind “long shower”. So when I tell them I’m off to take a long relaxing shower it comes out very naturally. I am not consciously lieing.
Also you can find other activities which can be used as a mask/cover. Innocent lies like these don’t hurt anyone.
2. If I trusted the guys I would tell them I’m doing exercises to improve EQ,hardness, whatever. That doesn’t sound that amazing and unbelieveble like making your dick bigger. (Or you can tell them you’ve read mantak chia’s book and try to apply some of that stuff)
3. Read a massage book. Learn some basic skills. Tell the guy you are studying self-massage. You use oil and you don’t want to make a mess, so you do it in the bathroom. Leave the Massage Tutorial PDF open on your computer desktop.
A few ideas, hope they come in handy. One room mate is no big deal. My room mates might think I’m masturbating. As if iCare. Many things in life are a big deal because we’re making them so. Good luck