[H]Abandon prayer intentionally — grave sin; some scholars consider it kufr.
[h]Delay prayer beyond its time without valid excuse.
[h]Rush through prayer without tuma'ninah.
[h]Look around or play with clothes during prayer.
[h]Pray when food is ready or you need the bathroom. (Muslim 560) (extra):
[h]Pass in front of someone praying without a sutrah. (Bukhari 510) [h]Crack knuckles or fidget during prayer.
[h]Leave a gap in the prayer row.