The full meaning of the word ridiculous is the meaning of stupid or arousing or deserving ridicule, extremely silly or unreasonable, absurd, preposterous.
When something is ridiculous it's deserving of or inviting derision or mockery and is absurd.
To some people the word ridiculous can be seen as offensive.
However the word ridiculous is not offensive at all and just means that something can be stupid or arousing or deserving ridicule, extremely silly or unreasonable, absurd, preposterous.
If someone does something that you think is ridiculous when they don't think it is and you say that to them that it is ridiculous then they may take offense to it.
For example if you tell someone they have a ridiculous outfit on and they actually like the outfit then they may be offended at you saying the word ridiculous to them.
But it's not always offensive to say something is ridiculous because some things are ridiculous even if they are funny and meant to make you laugh.
A clown could do something ridiculous to make you laugh and in that case the ridiculous word would not be offensive.