[Lil Bastrd]

Figure out something you can train your brain to fall back on. The 'finger gun' is just a unconscious habit. It's like people who chew their nails. They know they are doing it to some degree. It's a habit though. Something they do without thinking. It's the same with verbal things. Think high school the word "like" was used every two words. Mine a year ago was "no problem". I'd say it in response without planning on saying it. It was hard but I made the effort to change it. With your good friends, g/friend, and family talk to them. Ask them to use a word or look to trigger to you that you're doing it. Then it's up to you to catch yourself and to do something else.
Honestly though who cares if ppl think it's funny. It makes you unique.