Tokidoki is fun. I've also found that nani is infectious. I have friends and family members who use it even though they don't know any other Japanese. My favorite phrase is shinpaishinakutemoii. Don't worry!
Daijoubu だいじょうぶ is by far my favorite. When I was in Osaka for study abroad, my Japanese friends and I made up a saying for it; "DJB." Haha! So they would be like, "Oh its DBJ." So awesome.
I'm not sure if I love "ano", but it leaks into my everyday world. Annoying! One I find hilarious (merely for the translation) is "Teishukanpaku" - it means tyrannical husband.
One of the very first things I learnt was itterashai. Oh, and itadakimasu. I like them because they really illustrate differences between the UK and Japan.
ちよだい This is a fabulous word my first graders use(hope I spelled that right??) I love it when They are super informal with Their teachers and yell this.