This is easy! These days, you must attach to the internet. The funny sayings are everywhere on social media. People nowadays like to turn funny pictures with funny captions and some people also like to share funny moments through videos. You can also get the ideas taken from quotes from your favorite comedy movie or TV shows, as you can watch them on an online streaming platform or TV channel. Some people might as well excerpt the funny quotations from songs and books. If you like to be more creative, you can turn your funny moments into words for this.
You are free to put funny sayings on greeting cards. You can give such greeting cards for informal purposes, such as for best friends, neighbors, and family members. There are a lot of thematic greeting cards like Christmas funny cards, birthday cards, and even baby shower and wedding cards. You can get the wordings from online sources and book that full of funny riddles. It would be better if the cards are designed and written by the senders to add more personal touch.
You can divide it into some categories about appearance, season, food, and many more. You can say something like "My pillow gives me a free hair treatment every day." For the seasonal one, you can write "It's sweater weather, it'd be perfect to pull the blanket again because I'm too cool to get up." Another random funny quote you can say is "I will order this pizza at 11 because I know it'll arrive next year due to the long queue."
Basically, you can write funny sayings anywhere when you feel happy and humorous. You will have feelings usually after attending a party, meeting your best friends that know you too well and watching comedy shows on TV. In most cases, you write funny quotes at home when you remember those moments. If you are still a student, you can also write these at school for an assignment or just for fun. Some people make a living as a comedian. They must be mastering the skills to write these humorous sayings. They are either write it at home, at work, or in any public places they are performing at.