Start going out. I will become normal behavior instead of unusual behavior. Or just tell the truth. "Mom, I'm going out to get laid" is pretty normal behavior for a twenty six year old, or 36, or 46......

That it's none of their damn business where you are going!

Re: Better excuses....

I am in the same position as you except instead of a younger brother, it is a younger sister. I also am a bit younger than you too. I do not have to give any reason as to why I am leaving the house though, which is a good thing for me.

It is good to know that I am not the only one who is doing this while still living with my mom though, haha.

As for excuses I think the other guys pretty much covered it... As for the "I am going out on a date excuse", I do not think that will work well because it will just bring up more questions from your mom, such as... "How did it go?" etc...

I had that problem years ago & it pretty well stiffled my social life until I (disasterously) took up with an older (35) married woman I met through the family business.  In the end it was like the elephant in the room, everyone knew & no one talked about.  
I left the business for a while, the buisiness lost a customer...  and I boinked her on & off for 5 years.  She was never going to leave the hubby so I ended it.
Then I married someone else who saw me as a meal ticket...  also ended disasterously.  


OK, back to the subject at hand.  You don't want to say anything where little bro will want to come along.  
You should begin it assert yourself & just say you need time with others out of the family to stay well rounded.  Don't tell them in advance where you're going.  
Don't claim you saw a movie if you didn't.  You could go to a movie after or something.
You could go to a library (check the hours, be sure they're open.)  
I'm a regular at a local diner, coffee & a snack.  (Bring home donuts or muffins.)
Pretend to have dates.  Is there a social hang out?  Is there a nearby college?  

"No offense but I need time with others, outside the family."
jtp  

Re: Better excuses....

How about I'm going out I'll see ya later. lol I wish you luck thats tuff.

If you are living at home with your mother, why not set up an evening appointment.  

How about:

1.  I have a date.
2.  I am meeting some friends for a drink.
3.  I'm feeling restless.  Maybe I'll go out for a while and clear my head.

I don't see why you are having problems.  Most young adults don't stay at home every evening with the family.

for your freshly showered look when you return home.