I just booked a flight ticket on AirAsia for my friend and filled out the wrong gender carelessly. Is it a problem?
I didn't find their customer service phone numbers on AirAsia.
According to this tweet exchange the airline has no problem changing the title on tickets (March 2016).
No, it's not a problem, and you don't have to change it. I've flown on European flights a couple of times with the wrong gender selected for my travel partner and not one airline bat an eye. If you search on Flyertalk you will find other reports confirming the same. Likewise airlines don't care if your passport number or date of birth is invalid when entered during online check-in.
Just make sure the name is correct and you're good to go.
I just flew with Gulf Air and my ticket/boarding pass was labelled Mr when I'm clearly a female. The default gender was Mr on the website when I purchased the ticket, and there was no attention drawn to gender choice at that time. I emailed them and was told it would cost US$25 to change the gender and the Gulf Air person indicated that I should do so. As this was about 10% of the flight cost, I decided to wait and do it at the airport if there was a problem. Thankfully, no-one commented on it at any time.